corundum

corundum
Red corundum on garnet amphibolite from Winza in Mpwapwa District , Dodoma Region , Tanzania . Size: 3.8 × 3.1 × 2.3 cm.
General and classification
other names	Adamantine Adamantine Spar (Demantspath / Diamantspat) Adamas siderites Anthrax Harmophane (Corindon harmophane) Hard spar, hard spar Italian Girasol Naxium, Naxium ex Armenia Salamstein Emery (Schmergel, Smergel, Smirgel, Smiris, Smyris) Soimonit Télésie Zircolite
chemical formula	Al 2 O 3
Mineral class (and possibly department)	Oxides and hydroxides
System no. to Strunz and to Dana	4.CB.05 ( 8th edition : IV / C.04) 04.03.01.01
Similar minerals	Spinel
Crystallographic Data
Crystal system	trigonal
Crystal class ; symbol	ditrigonal-scalenohedral; 3  2 / m
Space group	R 3 c (No. 167)
Lattice parameters	a  = 4.75  Å ; c  = 12.98 Å
Formula units	Z  = 6
Frequent crystal faces	{10 1 1}, {0001}, {11 2 0}, {11 2 1}, {22 4 1}, {22 4 3}
Twinning	lamellar parallel {10 1 1}; rarely contact or penetration twins after {0001} or {10 1 1}
Physical Properties
Mohs hardness	9
Density (g / cm 3 )	3.98 to 4.10 (measured); 3.997 (calculated)
Cleavage	missing, but divisible according to {10 1 2} and {0001}
Break ; Tenacity	shell-like to splintery; brittle
colour	colorless, colored variably due to impurities, almost all colors are possible
Line color	White
transparency	translucent to transparent, emery is opaque
shine	Glass to diamond shine, often a little "greasy"; Pearlescent luster on the base and on secretion surfaces; Silky shine on star sapphire / ruby, Girasol and sapphire / ruby ​​cat's eye
Crystal optics
Refractive indices	n ω  = 1.767 to 1.772 n ε  = 1.759 to 1.763
Birefringence	δ = 0.008 to 0.010
Optical character	uniaxial negative, often abnormally biaxial
Axis angle	2V = ≤ 58 ° (measured)
Pleochroism	clearly from O = pale to deep blue to E = blue-green to yellow-green or from O = deep purple to E = pale yellow (stronger pleochroism with colored corundums)
Other properties
Chemical behavior	Not attacked by acids (except phosphoric acid and sulfuric acid), but dissolved by potassium disulphate. Blue color of the powder moistened with cobalt solution and calcined for a long time.
Special features	Rare but strong luminescence . Occasionally chatoyance , asterism and color change (alexandrite effect).

The corundum is a relatively common occurring mineral from the mineral class of oxides and hydroxides . It crystallizes in the trigonal crystal system with the chemical composition Al ₂ O ₃ and is therefore, chemically speaking, aluminum oxide .

Corundum is the reference mineral for Mohs hardness 9 on the Friedrich Mohs scale, which goes up to 10 ( diamond ) . It usually develops long, prismatic or columnar to barrel-shaped crystals , but also granular aggregates that can have different colors depending on the contamination. In chemically pure form, corundum is colorless. Well-known varieties with the same composition and crystal structure are ruby (red due to traces of chromium) and sapphire (different colors, including blue due to iron or light red due to titanium).

The surfaces of the translucent to transparent crystals have a glass-like to diamond-like, often slightly greasy sheen . Corundum has no cleavage , but very perfect segregation after the twin surfaces, which have a pearlescent sheen. Due to its brittleness , it breaks like glass or quartz , with the fracture surfaces being scalloped to splintery. The largest corundum crystals known to date reached a length of about one meter and a weight of up to 152 kg.

Corundum is one of the most important industrial minerals and is widely used due to its high chemical and temperature resistance as well as its high hardness and abrasion resistance . In addition, the colored varieties of corundum have been expensive and highly valued gemstones from ancient times (see use ).

Corundum is also produced artificially. The material obtained in this way is used as an abrasive (sandpaper, cutting discs, etc.) and as a blasting agent because of its great hardness .

Etymology and history

Probably the first mention of the mineral, which is known today as corundum, comes from Pliny the Elder . In the 37th book of his Naturalis historia he reports on Adamas siderites , which is very probably corundum.

The name corundum comes from the Tamil குருந்தம் kuruntam , which in turn is related to Sanskrit कुरुविन्द kuruvinda . In the Indian languages, this actually means the ruby .

The name Corinvindum was first used by John Woodward in 1719 .

Nella corivindum is found in fields where the rice grows: it is commonly thrown up by the field rats, and used, as we do emery, to polish iron… Tella Convindum Fort St. George. Mr. Bulkley. This is a talky Spar, gray, with a cast of green. It is used to polish Rubies and Diamonds.

“ Nella corivindum is found in fields where the rice grows; it is usually churned up by the field mice and, like our emery, used to polish the iron ... Tella Convindum Fort St. George. Mr. Bulkley. It is a talcous spatula of gray blending into green; it is used to polish rubies and diamonds. "

- John Woodward : A Catalog of the foreign fossils In the Collection of J. Woodward MD

John Woodward, English physician , geologist and natural historian . The name Corinvindum / Corinvendum for Corundum (English for corundum) goes back to him .

In Woodward's addendum to the above list, which appeared in 1725 and in which he changed Corivindum to Corivendum , you can read on page 6:

Nella corivendum is found by digging at the Foot or Bottom of Hills, about 500 Miles to the Southward of this Place. They use it, as Emery, to clean Arms, & c. It also serves to grind Rubies, by making it like hard cement, by the help of Stic-Lac mix'd with it. East India . Mr. Bulkley .

“ Nella corivendum is found digging at the foot of hills about 500 English miles to the south of the place mentioned, and is used as emery for cleaning rifles. You can also use it to grind ruby ​​by connecting it with an adhesive varnish and thus turning it into a kind of hard cement. East India . Mr. Bulkley . "

- John Woodward : An Addition to the Catalog of the Foreign Native Fossils In the Collection of J. Woodward MD

These are apparently the only mentions of this mineral by an author prior to 1768 , along with some other notes in the Woodward register. As reported by Charles Francis Gréville , "Vice Chamberlain of the King of England and a member of the Royal Society," the famous jeweler William Berry in Edinburgh by a Dr. Anderson from Madras in India a delivery of crystals "with information of their being the material used by the natives of India to polish crystal, and all gems but diamonds" ( German  "with the information that this material was used by the Indian natives for polishing crystals and all precious stones are used with the exception of diamonds ” ). Although Berry was able to work well with the material sent to him, agate , carnelian and other stones, he found that this work could be carried out much better with the harder diamond , which justified the significantly higher price for diamond. The stones from Madras were therefore set aside as a mere curiosity.

Greville mentions a Dr. Black, who recognized that these crystals were different from all stones known in Europe up to this point in time and who called them "Demantspath" because of their hardness. “In 1784, however, Colonel Cathcart from India sent me his true maiden name Corundum, along with a few copies that he had received from D. Anderson and which I shared for analysis. As soon as only the original name of this fossil was known, it emerged from D. Woodward's Catalog of Foreign Fossils, which had appeared in 1719, that the same fossil had already been sent to him by his correspondent Mr. Bulkley from Madras. "

Richard Kirwan used the English spelling of the name Corundum , which is still valid today, in 1794 and Charles Gréville in 1798/99. Martin Heinrich Klaproth , who had also received material from Gréville, translated in 1786/87 the name given by English naturalists around 1780 Adamantine Spar or Spath adamantin with Demantspath . Initially, Klaproth considered the main component of the mineral to be a new earth, the Demantspatherde or Corunderde , but later found that the mineral mainly consists of alumina , i.e. aluminum oxide. Klaproth found the same composition for the sapphire.

Two-tone pink-violet sapphire in the host rock from Ihosy in Madagascar (size: 6.8 cm × 4.5 cm × 4.4 cm)

In contrast to what has been written so far, René-Just Haüy reports in 1801 that the knowledge of corundum was passed on to Doctor Lind , a member of the royal family. Societät zu London, who discovered it in China in granite rocks, in which it grew in feldspar, mica and soapstone. Haüy further reported that Corindon was also found in granitic rocks near Philadelphia and on the southwest coast of India near Malabar . He had received material from the latter deposit from Charles Gréville. Haüy combined ruby ​​and sapphire under the new term Télésie (from ancient Greek τἐλειος, τελήεις teleios , German 'perfect' ), but withstands emery as a separate type of mineral under the term fer oxydé quartzifere . However, he mentions the Corindon as a synonym for the Spath adamantin , which has been known since around 1780 , as a completely independent species. In 1802, Count Jacques Louis de Bournon wrote the classic “Description of the Corundum Stone and its varieties”.

Following Dietrich Ludwig Gustav Karsten (1800), Franz Ambrosius Reuss published his textbook of mineralogy in 1802 "according to the OBR Karsten mineralogical tables", in which he as an independent mineral species ("genera") the "diamond spath " ( Spathum adamantinum , Spath adamantin , Spate adamantino , Adamantin spar ), the “Korund” ( Corundum , Corindon , Corundumstone ), the “Rubin” ( Rubinus , Rubis , Rubino , Ruby ) as well as the “Saphir” ( Saphirus , Saphir , Zaffiro , Sapphire ) are mentioned.

In his “Handbuch der Mineralogie” published in 1811, Christian August Siegfried Hoffmann treated “sapphire” (including “ruby”) as well as “emery”, “corundum” and “Demantspath” as independent minerals and gave the following reason: “Initially believed one can say that corundum and demantspath constitute a single genus, and Mr. Hauy, the Count of Bournon, as well as several other mineralogists, are of the same opinion. However, due to their differences in the proportions of color, gloss, breakage, transparency and occurrence, Mr. Werner was prompted to list them as two different types. "But just two years later Friedrich Hausmann combined both the noble corundum and" Demantspath "And emery under one name, the" corundum ".

Unlike the term “corundum”, the name “ruby” appears as early as the 12th century in Provence and from 1250 in Germany in the legends of Parzival , for example in Wolfram von Eschenbach's Parzival . First, with him and called carbuncle called (carbunculus) in general, red gems. The name "sapphire" (from ancient Greek σάπφειρος sappheiros , German 'sapphire' ) is given as a loan word from the East and interpreted in different ways. In antiquity, the term sapphire was used to describe the lazurite stone , later this term was transferred to other - always blue - minerals, most recently to the hard, blue, transparent corundum. The assignment of the names ruby ​​and sapphire to corundum only took place at the turn of the 18th and 19th centuries. Century, when - through analyzes by Martin H. Klaproth - the material identity of ruby ​​and sapphire with corundum was recognized.

classification

Bluish violet corundum (sapphire) from "Zazafotsy", Ihosy District, Fianarantsoa Province , Madagascar . Size: 9.1 × 5.3 × 4.0 cm.

In the now outdated, but still in use 8th edition of the mineral classification according to Strunz , corundum belonged to the mineral class of "oxides and hydroxides" and there to the department of "oxides with metal: oxygen = 2: 3", where it, together with eskolaite , hematite and Karelianit formed a separate group.

The 9th edition of Strunz's mineral systematics, which has been in effect since 2001 and is used by the International Mineralogical Association (IMA), assigns corundum to the extended class of "oxides (hydroxides, V ^[5,6] vanadates, arsenides, antimonides, bismuthides, suldides, Selenide, Telluride, Jodide) ”and there in the section of“ Metal: Oxygen = 2: 3, 3: 5 and comparable ”. This section is further subdivided according to the size of the cations involved , so that the mineral can be found according to its composition in the sub-section “With medium-sized cations”, where it is named after the “corundum group” with the system no. 4.CB.05 and the other members brizziite , ecandrewsite , eskolaite, geikielite , hematite, ilmenite , karelianite , melanostibite and pyrophanite as well as the minerals auroantimonate and romanite which have not yet been confirmed by the IMA .

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns corundum to the class of "oxides and hydroxides" and there in the "oxides" category. Here, together with Hematite, he is the namesake of the "corundum-hematite group" with the system no. 04.03.01 and the other members Eskolait, Karelianit and Tistarit can be found in the subsection “ Simple oxides with a cation charge of 3+ (A ₂ O ₃ ) ”.

Chemism

Magenta-colored corundum (sapphire) from "Zazafotsy", Madagascar. Size: 5.5 × 4.2 × 3.3 cm.

Corundum is chemically almost pure Al ₂ O ₃ with 53.04% aluminum and 46.96% oxygen , in which magnesium , titanium , vanadium , chromium , iron and gallium and rarely also elements with high valencies ( HFSE ) such as niobium , tin , Tantalum and thorium always occur, but only in traces. For chromium, contents of 1–2.5% by weight Cr ₂ O _{3 are} reported.

Corundum is the Al-dominant analogue of Cr-dominated eskolaite, Fe-dominated hematite and V ³⁺ -dominated karelianite. Due to the high proportion of homopolar bonds, corundum has little tendency to form mixed crystals . With Fe ₂ O _{3 there} is complete miscibility above 1400 ° C, with Cr ₂ O ₃ above 1080 ° C.

Corundum easily converts into other aluminum minerals such as zoisite , sillimanite , kyanite and especially margarite , less easily into diaspore (kayserite), gibbsite , andalusite , spinel , chloritoid and muscovite . From Perth in Ontario , Canada , up to 10 cm long pseudomorphoses of a pale green, greasy-feeling substance like corundum are described, which is scapolite , which in turn has been replaced by pinite (muscovite). Spinel pseudomorphs are known from Bathurst Township, Lanark County , also in Ontario, Canada. Pseudomorphoses from muscovite to corundum, which are designated by their own name "Damourite", are quite common.

Crystal structure

Crystal structure of corundum

Crystal structure of corundum as viewed along the b-axis [010].
__ Al ³⁺     __ O ²⁻

Corundum crystallizes trigonal in the space group R 3 c (space group no. 167) with the lattice parameters a  = 4.75  Å and c  = 12.98 Å as well as six formula units per unit cell .

In the corundum structure, the oxygen atoms form a slightly distorted hexagonal closest packing of spheres , in which two thirds of the octahedral gaps are occupied by trivalent aluminum ions. The octahedra have common edges and in this way form rings of six, which are arranged parallel to gibbsite-like layers or layers (0001). The layers are connected to form a framework by common surfaces and corners of the octahedra. Since every two octahedra have a common area, two neighboring Al ³⁺ ions are only 1.36 Å apart. The Coulomb bond is superimposed by strong homopolar bond components, which explains the high hardness of the corundum.

The oxygen atoms form layers of the closest packing, which are stacked in two layers on top of each other (ABAB ..., hexagonal close packing of spheres). Between every two of these layers there is an aluminum layer C, in which every third place is unoccupied. The Al atoms of a layer form six-membered rings, the centers of which are unoccupied. The Al layers can occur in three layers, which are implemented one after the other (layer sequence A'B'C'A'B'C '...). The aluminum atoms are octahedral surrounded by six oxygen atoms. In the ideal case (no influence of the vacancies in the aluminum layers), the oxygen atoms would be trigonal prismatic surrounded by four aluminum atoms and two vacancies. The displacement of the aluminum atoms resulting from the vacancies results in a distorted tetrahedral coordination of the oxygen atoms of four aluminum atoms.

In addition to α-Al ₂ O ₃ , the oxides Ti ₂ O ₃ , V ₂ O ₃ , Cr ₂ O ₃ , α-Fe ₂ O ₃ , Rh ₂ O ₃ and α-Ga ₂ O ₃ as well as crystallize in the corundum structure the chemical compounds γ-Al ₂ S ₃ and Co ₂ As ₃ .

properties

morphology

Corundum usually forms ingrown, prismatic, steep pyramidal, tabular, rhombohedral and rarely also needle-like, often coarse crystalline crystals weighing up to 150 kg. Generally sizes of up to one meter are given. The crystals often represent combinations of the most important basic shapes. These include prisms such as {10 1 0} and {11 2 0}, dipyramids such as {11 2 1}, {22 4 1}, {22 4 3} and {14.14. 28 .3}, rhombohedra like (10 1 1) and (10 1 2), the basic pinacoid {0001} and ditrigonal scalenohedra . The interaction of several differently steep dipyramids such as {11 2 1}, {11 2 3} and {44 8 3} result in spindle- to barrel-shaped and horizontally striped to strongly grooved crystals.

• Costume and habit of corundum crystals (the same colors mean the same surface shapes)
• 

  1. long prismatic according to {11 2 0}

• 

  2. prismatic, from "Ceylon"

• 

  3. short prismatic, from "North Carolina"

• 

  4. flat panel

• 

  5. rhombohedral, from "Burma"

• 

  6. Rhombohedral, little area

• 

  7. steep rhombohedral with {14.14. 28 .3} as the supporting form

• 

  8. steep rhombohedral with {22 4 1} as the supporting form

• 

  9. steep pyramidal, extremely poor in area, from "Selankina"

• 

  10. steep pyramidal, extensive area, from "Chester, Mass."

• 

  11. pyramidal, little area

• 

  12. spindle-shaped, extensive

• 

  13. extensive and barrel-shaped, from the "Ilmen Mts."

• 

  14. extensive and barrel-shaped

• 

  14. extensive and barrel-shaped

Twinned corundum crystal from Ratnapura, Sabaragamuwa, Sri Lanka

Twins with (10 1 1) as the twin plane often only appear in the form of thin corundum lamellae, which cause excellent twin stripes. If the lamellae are switched on parallel to all rhombohedral surfaces, this leads to a striation on the surfaces of the basic pinacoids {0001}. Contact or penetration twins according to {0001} or {10 1 1} are rare . The latter are arrowhead-shaped twins made of two tabular corundum crystals according to {11 2 0}, as described from the Transvaal.

Finally, corundum also occurs in the form of coarse late masses, in unrolled grains as well as grainy and massive (rock-forming as emery).

physical and chemical properties

In its pure form, corundum is colorless, but due to foreign admixtures it can be gray, brown, pink to pigeon blood, orange, yellow, green, blue to cornflower blue or purple, as well as blotchy or colored. Corundum is a prime example of an allochromatic mineral.

Not all trace elements contained in the corundum act as chromophore and influence the color of the corundum (e.g. gallium). The color of the corundum depends on the presence of chromophores and in some cases (especially in the case of yellow shades) on the appearance of color centers .

Contents of chromium lead to red and pink tones, of titanium and iron to blue colors, of iron alone to blue, greenish-blue, yellowish-green to yellow colors and of vanadium to violet colors (with a color change effect). Appropriate mixtures of chromophores can produce almost all color tones in the spectrum with the exception of pure green colors, which are only known for synthetic corundum.

The individual hues are caused by the mechanisms listed below: Violet: by Fe ²⁺ -O-Ti ⁴⁺ charge transfer, coexisting with Cr ³⁺ in octahedral coordination. Blue : by Fe ²⁺ -O-Ti ⁴⁺ charge transfer with the influence of Fe ²⁺  → Fe ³⁺ charge transfer. Green : by Fe ³⁺ in octahedral coordination, coexisting with Fe ²⁺  → Ti ⁴⁺ charge transfer and Ti ³⁺ and Cr ³⁺ in octahedral coordination. Yellow : by O ²⁻  → Fe ³⁺ charge transfer; by Fe ³⁺ and Ti ³⁺ , which leads to a large number of unstable color centers of unknown structure; by Fe ³⁺ pairs. Orange to orange-brown : due to Cr ³⁺ in octahedral coordination and color centers; with participation of Fe ³⁺ . Orange pink (“Padparadscha”): by Cr ³⁺ in octahedral coordination and color centers, Cr ⁴⁺ in octahedral coordination by substituting Cr ⁴⁺ and Mg ²⁺ for Al ³⁺ in the crystal structure. Red (ruby): by Cr ³⁺ in octahedral coordination with minor participation of V ³⁺ and Fe ³⁺ in octahedral coordination. Pink : by Cr ³⁺ in octahedral coordination. Color change : due to Cr ³⁺ and / or V ³⁺ in octahedral coordination in a special concentration range.

Regardless of the color, the line color of the corundum - in this case the color of its powder - is always white. The surfaces of the translucent to transparent crystals have a glass-like to diamond-like, often somewhat greasy sheen , which agrees well with the values ​​for the refraction of light . The crystals often show a pearly luster on the base and on the secretion surfaces; Star sapphires / star rubies and sapphire / ruby ​​cat's eyes have a satin sheen due to the enclosed rutile needles.

High values ​​for light refraction (n _ω  = 1.767 to 1.772; n _ε  = 1.759 to 1.763) with clear relief and a low value for birefringence (δ = 0.008 to 0.009) were identified on the crystals of the corundum .

The highest values ​​for light refraction (n _ω  = 1.768 to 1.780; n _ε  = 1.760 to 1.770; δ = 0.008 to 0.010) have so far been measured on rubies from Malawi.

Corundum (blue core), biotite (brown) and hercynite (green) in a Mafic Microgranular Enclave in the granite of S. Andrea, Elba, Italy. Field of view 2 mm.

In transmitted light, corundum is colorless, pale bluish or reddish and can be recognized by its clear relief and - as with quartz - gray interference colors of the first order. Under the microscope , the mineral can show clear to strong pleochroism, especially in colored stones, from O = pale to deep blue to E = blue-green to yellow-green or from O = deep purple to E = pale yellow.

Colored corundums show stronger pleochroism, e.g. B. Ruby from intense violet-red to light orange-red, blue sapphire from purple-blue to light greenish-blue, orange-colored sapphire from orange to light yellow-brown or pale orange, purple (red-blue) sapphire from purple to orange, yellow sapphire from yellow to pale yellow, green sapphire from green to blue-green and yellow-green and pink sapphire from pink to pale pink or more red.

Corundum apparently has a perfect cleavage according to {10 1 2} and a less clear cleavage according to {0001}, both of which represent only secretions after the twin surfaces due to separated boehmite (divisibility according to the rhombohedron). It breaks but similar because of its brittleness quartz or Vesuvianite , wherein the fractured surfaces are formed conchoidal to splitterig. Corundum is not brittle in coarse masses, but on the contrary is very tough. Corundum is the reference mineral on the Mohs hardness scale for Mohs hardness 9. It is after diamond (C, hardness 10) and the very rare minerals moissanite ( SiC , hardness 9.5) and qingsongite (cubic BN , hardness 9-10) ) the fourth hardest mineral. It shows a clear anisotropy of hardness with a lower hardness in the direction of the main axis than in the other directions. The measured density for corundum is 3.98 to 4.10 g / cm³, the calculated density is 3.997 g / cm³.

Corundum containing chromium shows intense fluorescence , even in blue and yellowish stones. Orange, peach or apricot-colored fluorescence is caused by superimposing the fluorescence caused by Cr ³⁺ with a greenish-yellow fluorescence band , which is probably due to defect centers . Broken down according to the wavelength, a very strong red fluorescence can be observed for corundum in long-wave UV light (λ = 365 nm) and a medium-strength red, violet-red, violet-pink or orange fluorescence in short-wave UV light (λ = 254 nm) . Afterglow ( phosphorescence ) is also often observed.

Corundum under long-wave UV light with intense red fluorescence. Chit Island near Polyarnyj Krug, North Karelia, Russia.

The color and strength of the fluorescence varies with the location, for which v. a. the Fe content should be responsible.

• Ruby from Myanmar: Intense red through Cr. The best stones fluoresce in strong sunlight.
• Ruby from Thailand: Less intense red due to Cr + Fe. Occasional mottled blue fluorescence when heat treated.
• Ruby from Sri Lanka: Strong orange-red fluorescence in long-wave UV light, less strong in short-wave UV light (Cr).
• Pink sapphire: As above
• Padparadscha: As above. Heat-treated stones can fluoresce strongly reddish orange in short- and long-wave UV light.
• Green and most of the yellow sapphires: No fluorescence (Fe + Ni + Ti).
• Blue sapphires: none (the majority, due to Fe + Ti) to red or orange fluorescence (Kashmir, Sri Lanka, Montana) in long-wave UV light. Heat-treated stones can show a dull green fluorescence in short-wave UV light.
• Colorless: Moderate light red to orange fluorescence.

The long-known thermoluminescence is very typical of corundum . Even with a low supply of heat, red corundums glow yellow and cloudy gray corundums are bluish. Under the influence of cathode rays, corundums give off a red-yellow light, artificial rubies do not show this.

Corundum remains unchanged before the soldering tube , but can be melted with oxygen to form a reddish pearl with a crystalline surface. In borax and phosphorus salt it slowly dissolves to a clear, non-opalescent glass, which in the absence of iron also remains colorless. He is also not attacked by soda . The fine mineral powder turns blue after prolonged heating with cobalt solution in the oxidizing flame. From phosphoric acid , H ₃ PO ₄ , completely dissolved when heated until it begins to volatilize. Soluble in sulfuric acid when heated in a closed glass tube in a mixture of eight parts SO ₃ and three parts water to 210 ° C. Easily meltable with potassium disulfate to a water-soluble mass.

The melting point of the corundum is 2040 ° C. At 25 ° C the thermal conductivity is 41.9 W / (m · K) and the heat capacity is 754 J / (kg · K).

Red noble spinel can look very similar, especially when unrolled in soaps, which in earlier times repeatedly led to confusion. The ruby of the Black Prince , which is located above the Cullinan II in the Imperial State Crown , part of the British Crown Jewels , is also just a polished, 5 cm high spinel . Such pale red and pink spinels were called "balasrubin" (Rubis balais), but this misleading name should no longer be used.

Corundum and above all ruby ​​can be easily distinguished from all other (red) minerals based on their hardness, density and optical properties.

Modifications and varieties

Corundum is a modification of aluminum oxide (α-Al ₂ O ₃ ). In addition to corundum, there are three other polymorphs . Delta lumite is the tetragonal analogue of the trigonal corundum. Further polymorphs are the as yet unnamed phases UM1990-23-O: Al, θ-Al ₂ O ₃ , and UM1990-24-O: Al, σ-Al ₂ O ₃ .

For a long time, the color varieties (color variations due to small amounts of metallic additions) of corundum have been given their own names. Red corundum “ruby” and pink-orange corundum “Padparadscha” are called. All other colored corundums are called "sapphire".

Color variations due to foreign ions

• Ruby - strong red ("pigeon blood red") thanks to chrome (1–2.5% Cr ₂ O ₃ )
• Sapphire - deep blue through iron and titanium, furthermore all colors except red; brown through iron, gray, pink, yellow, green, purple
• Padparadscha - pink-orange. Name after Sinhala padma raga , the color name for a local lotus flower.
• Leucosapphire or water sapphire is colorless sapphire.

• 

  Ruby from Mogok, Mandalay, Myanmar

• 

  Blue sapphire from Mogok, Mandalay, Myanmar

• 

  Blue-violet sapphire from Zazafotsy, Fianarantsoa, ​​Madagascar

• 

  Lavender-colored sapphire from the Hunza Valley, Gilgit-Baltistan, Pakistan

• 

  Yellow-orange sapphire from Ratnapura, Sri Lanka

• 

  Star ruby ​​- cabochon with asterism

• 

  Star sapphire - cabochon with asterism

• 

  Emery from Naxos island, Greece

• 

  Ruby and Zoisite as Anyolite

Further - in some cases - superfluous color names for corundum:

• Blue Alexandrite (German: Blauer Alexandrite) is a trade name for blue / violet color-changing sapphires.
• With Barklyit a magenta Rubinvarietät is called, originally, was first known from Victoria, Australia.
• Chlorosaphir (from ancient Greek χλωρὀς chloros , German 'green' ) is a green corundum from the ejections of the Siebengebirge.
• Indigo sapphire (or lynx sapphire or cat sapphire ) are called very dark sapphires according to Max Bauer .
• Ledo frozen fire is a Fe-Ti-rich blue gem variety of corundum.
• Oriental amethyst is a purple variety of corundum gemstone.
• Oriental emerald is a green gem variety of corundum.
• Oriental topaz is a yellow variety of corundum gemstones.
• Padmaragaya is a trade name for a yellow variety of corundum gemstones.
• Anthrax (not to be confused with the disease anthrax ) are called red spinels and certain rubies.
• With Soimonit were by Johann Nepomuk von Fuchs Senator Soimonow dark sapphire blue corundum crystals from the soaps of Barsowka in 1823 in honor of Chelyabinsk region in the southern Urals called.

Varieties by inclusions

• Star sapphire and star ruby are corresponding corundums with asterism . Oriented, d. H. parallel to the a-axes, embedded acicular rutile or hematite - ilmenite causes a more or less perfect, six-pointed star-shaped reflection that glides over the surface when the stone is moved. Very rare are twelve-pointed stars that are formed by a combination of both types of inclusion.
• Italian Girasol , sapphire cat's eye , is an opalescent sapphire with a rounded light instead of the star. Anselmus de Boodt had already mentioned him in 1609 ("De Asteria [Germanice Sternstein], aut Solis gemma, Italis Girasole").
• Trapiche ruby (from Spanish trapiche , sugar mill ) are oriented, wheel-like intergrowths of several prismatic ruby ​​crystals. Six yellow, white or black "arms" extend from a core, forming a star, creating six triangular or trapezoidal sectors between the arms. The arms of the six-pointed stars consist of corundum, carbonates such as calcite and dolomite, or tiny, unidentified K-Al-Fe-Ti-silicates. Such features are typical of dendritic crystal growth such as e.g. B. in snowflakes . The trapiche rubies come from Myanmar and Vietnam.

Other varieties of corundum

• Chromian Corundum (German: Chromkorund) is an unnecessary name for a chromium-containing corundum, since most corundums contain chromium.
• Diamantspat ( English Adamantine Spar ) is a silky, brown corundum variety.
• As Hard saving , German: Hartspat next andalusite and corundum has been designated.

Artificially produced corundum with proper names

• Alundum is an artificially produced corundum used as an abrasive.
• As Zircolith a man-made white corundum is called.

Corundum-containing rocks with proper names

• Emery , also Schmergel, Smergel, Smirgel, Smiris or Smyris, is a fine-grained mixture of corundum with magnetite , hematite , ilmenite and quartz and therefore not a variety, but a rock . It is found in the form of large rock masses, especially on the Greek island of Naxos . Allegedly the material comes from Smyrna (today Izmir ), therefore by Pedanios Dioscurides as ancient Greek Σμύρις Smiris , German called 'Smyrna' . "Naxium" or "Naxium ex Armenia" is the same material already described by Pliny.
• Anyolite (also anyolite, rubinzoisite or zoisite rock) is a metamorphic rock, which consists of red, opaque corundum (ruby), green zoisite and often black minerals of the amphibole group (mostly Tschermakite ).
• Goodletite is a colorful metamorphic rock from the South Island of New Zealand consisting of fuchsite, margarite and the corundum varieties ruby ​​and sapphire.

Education and Locations

Educational conditions

Ruby accompanied by pyrite on marble from Lục Yên, Vietnam

Al-rich, Si-undersaturated geological environments are characteristic of corundum. You can find him:

• As a secondary part of alkali stones and in the form of large ingrown crystals in syenites , monzonites and nepheline syenites and their (mostly quartz-free) pegmatites such as B. in Ontario / Canada.
• As a side effect in peridotites such. B. in North Carolina and Georgia in the USA , in the anorthosite of Kyschtym in the Urals with 47% corundum, 38% plagioclase (An ₈₆ ), 10% biotite; in the hornblendegabbro of "Cima di Foggio" in the Ivrea zone in the Valsesia valley , Italy , with 12% corundum.
• Primarily or as a reaction product in eclogitic xenolites in kimberlites .
• In intramagmatic titanomagnetite deposits such as B. Ruoutevare, Kvikkjokk near Jokkmokk , Lapland , Sweden .
• During the contact and regional metamorphosis, emerald rocks made of corundum, magnetite, hematite, ilmenite and quartz were formed from SiO _2- poor parent rocks. B. in Izmir (Smyrna) / Asia Minor and on Naxos. Also in other metamorphic rocks such as dolomite or marble .
• In mineral associations with advanced argillic and hydrothermal alteration .
• Corundum cannot be chemically attacked on the earth's surface. Due to its weathering resistance, great hardness, lack of cleavage and the somewhat higher density compared to other silicates, it is enriched in weathering residues and soaps. Famous gemstone soaps with ruby ​​and emerald at Adam's Peak in Sri Lanka and at Mogok in Myanmar .

Typical accompanying minerals of corundum are, depending on the parent rock (here in the sense of rock containing usable minerals or precious stones), the feldspar anorthite and oligoclase , nepheline , scapolite (in syenites ); Spinel , rutile , chondrodite , "hornblende", phlogopite , calcite (in metamorphosed limestones ); Kyanite , sillimanite , dumortierite , “ chlorite ” (in slate ); Pyrope- rich garnets , spinel, phlogopite, omphacitic clinopyroxene , kyanite, rutile, graphite , diamond (in eclogitic xenolites); Hematite, magnetite, spinel, cordierite , Högbomite , garnet (in emery deposits ). The mineral is often found in soaps with other stable heavy minerals such as garnet, spinel, zircon, rutile, also emerald , tourmaline, topaz and kyanite.

Corundum and its varieties have so far been identified as a frequent mineral formation worldwide (as of 2018) at around 1500 sites. The river "Sudimani Spruit" at "Manuel's Kop" near Greater Letaba in the Mopani District , Limpopo Province in South Africa , where a 68.58 cm tall and 152 kg heavy crystal (today in the Museum of the Geological Survey in Pretoria), and Bancroft in the Canadian province of Ontario with a crystal find weighing around 30 kg.

Locations

A type locality is not defined for the mineral. In view of the very large number of locations where corundum was found, only a few, mainly larger crystal-producing locations can be mentioned here.

Europe

The best developed corundums in Germany come from the volcanic rocks of the Eifel in Rhineland-Palatinate . These include the "Emmelberg" near Üdersdorf not far from Daun ; the Ettringer Bellerberg near Ettringen not far from Mayen ; the "tub heads" near Ochtendung not far from Polch ; the Laacher Kessel in the Laacher See complex and the "Hüttenberg-Bimstuffe" in a tuff quarry between Dachsbusch and Hüttenberg near Glees not far from Niederzissen . In Saxony, corundum was found in the granulite of the type locality for Prismatin , the granulite outcrop Waldheim near Döbeln, and in the soaps of the sigh near Hinterhermsdorf not far from Sebnitz , Elbe Sandstone Mountains . The "Erzbaum Christi Fundgrube" and the "Drandorf Fundgrube" at the Ochsenkopf between Schwarzenberg and Sosa in the Erzgebirge mined emery until the middle of the 19th century.

Corundum was also found in Germany in the Black Forest and at the Kaiserstuhl in Baden-Württemberg; in the Bavarian and Upper Palatinate Forest in Bavaria; at the slag discovery site in Frankfurt-Heddernheim in Hesse; near Bad Harzburg in Lower Saxony; in several places in the North Rhine-Westphalian Siebengebirge as well as near Barmstedt and Schleswig in Schleswig-Holstein.

In Austria , well-developed corundum crystals were found primarily in the "Amstall graphite quarry" near Mühldorf , near Drosendorf and Wolfsbach, Drosendorf-Zissersdorf , and at the "Latzenhof" near Felling near Gföhl , all in the Waldviertel in Lower Austria . Also in pegmatites on Dürnberg near Ottensheim north-west of Linz , Urfahr-Umgebung district , Mühlviertel , Upper Austria , in the "Stubenberg granite quarry" near Stubenberg am See , Weiz district , and in the basalt (nepheline basanite) quarry near Klöch north-north-west of Bad Radkersburg , both in Styria and finally in crevices in the gneiss in the "Greinerrinne" on the southwest slope of the "Nasenkopf" in the Habach Valley , Hohe Tauern in Salzburg .

In Switzerland , corundum crystals up to 10 cm long are said to have come from the locality "Venett" (previously Passo Cadonighino), Campolungo, Val Piumogna , Leventina , Ticino, which has been known since 1813 . In the late summer of 1992 a new deposit with up to 6 cm long reddish crystals was discovered not far from the old site. Also in Ticino there are outcrops with corundum-containing pargasite amphibolite in the Valle d'Arbedo near Arbedo-Castione and east of it in Val Traversagna, Roveredo , Misox in Graubünden . Finally, in 1970 in the middle moraine of the Unteraar Glacier , Grimsel, Haslital , Bern , ruby ​​crystals up to 1 cm in size were found in amphibolite blocks embedded in fuchsite, which probably come from the Finsteraarhorn .

• 

  “Kleggåsen Ruby Quarry” at Froland, Aust-Agder, Norway

• 

  “Kleggåsen Ruby Quarry” at Froland, Aust-Agder, Norway

• 

  Marble quarry "Bianco Sivec" on Sivec, Prilep, North Macedonia

• 

  Marble quarry "Bianco Sivec" on Sivec, Prilep, North Macedonia

• 

  Miass in the Ilmen Mountains in the central Urals, Chelyabinsk Oblast, Russia

• 

  Chit Island at Polyarnyj Krug, Louchsky Rajon, Karelia, Russia

In Norway , a corundum-containing rock was discovered in 1956 near Froland , 11 km northwest of Arendal , Aust-Agder , which was quarried in the "Kleggåsen Ruby Quarry" for steps with red corundum crystals. Another important find in Norway was corundum-bearing mica schist on the west side of the Sagstuen River, Farsjø, Årnes, Nes .

Well-developed corundum crystals are known in Russia. a. from a deposit on the island Chit ( Russian Хит Остров, Полярный Круг, Лоухский район ) at Poljarnyj pitcher Louchskij Rajon, North Karelia, Republic of Karelia , Federal District Northwest Russia , from Rubinowoe Raj-Iz massif ( Russian Рай-Из массив Ямало-Ненецкий АО (Восточный склон Полярного Урала) ), Polar Ural , Federal district Ural , as well as in the area of Miass in Ilmengebirge in the central Ural , Chelyabinsk region .

In North Macedonia , 8 km north-northeast of the city of Prilep on the southwest slope of the Sivec mountain, which has been around for 500 years BC. d. "Bianco Sivec" dolomite marble quarries that are currently being extracted and contain idiomorphic corundum crystals in calcite veins.

On the island of Naxos, which belongs to the Greek Cyclades, the “Naxos Mine” is located near Drymalia in the municipality of Naxos and Little Cyclades. Before the Second World War it was producing 10,000 tons of emery a year . Further emery deposits are located in the Aperathos and Koronos areas on Naxos.

Other European sites are in Bulgaria , Finland , France , Greece , Ireland , Italy , Poland , Romania , Russia , Sweden , Slovakia , Ukraine , Hungary and the United Kingdom (Great Britain).

Asia

India is the classic corundum country, not least because the name has its origin in this country. That this is the case is mainly due to the fact that although the main part of the grinding corundum has always come from Ceylon or Burma, it came to Europe via India in earlier times. Nevertheless, corundum deposits can be found in various Indian states such as Andhra Pradesh (with deposits near Anantapur , in the Krishna district and near Kurnool ); Telangana (especially in the Hyderabad district ); Bihar ; Tamil Nadu ; Karnataka (formerly Mysore , here especially the Mysore district); Odisha (until 2011 Orissa, here mainly in the Kalahandi district ) and Jammu and Kashmir , here in the sapphire mines near Pádar, near Sumjam in the Kudi Valley and on Mount Nangimali in the Shonther Valley, Himalaya. Remarkable corundums are idiomorphic rubies up to 7 cm in size that occur in a ruby-bearing biotite-sillimanite gneiss near Alipur, Mysore.

• 

  Mysore District, Karnataka, India

• 

  "Carvatie", India

• 

  Sri Lanka

• 

  Ratnapura, Sri Lanka

• 

  Chumar, Ganesh Himal, Bagmati, Nepal

• 

  Hunza Valley, Gilgit, Gilgit-Baltistan, Pakistan

• 

  Jegdalek Ruby Mine, Sorobi, Kabul Province, Afghanistan

• 

  Mogok, Pyin Oo Lwin, Mandalay, Myanmar

• 

  Lục Yên, Yên Bái Province, Bắc-Bộ Mountains, Vietnam

For a long time, Sri Lanka provided a large part of the world's production. Soap deposits near Ratnapura ( Sinhala : රත්නපුර "City of Jewels"), Sabaragamuwa Province ; at Matale in the district of the same name and at Elahera in the central province , at Polonnaruwa in the district of the same name in the north-central province and at Galbkka, Wellawaya in the Moneragala district , Uva province . It is characteristic of the corunda of Sri Lanka that they are found in almost all colors and often show asterism, two- and multi-colored as well as alexandrite effects. In 1989, near Rakwana not far from Ratnapura, an extremely large sapphire crystal, terminated on both sides, weighing 40.3 kg and measuring 25 × 50 cm was found, which was grindable in some areas, but otherwise milky.

In Nepal , corundum was discovered by chance by goatherds in 1981. The find area with the “Chumar Ruby Mines” is located in the Ganesh Himal massif in the Dhading district , Bagmati administrative zone . Corundum, v. a. Ruby, is found in metamorphosed limestone as well as in slate. The colors of the corundum vary from pink to pink, reddish or blue-violet to the classic ruby ​​red. Often there are color zones in the form of dark purple to blue bands.

The most important corundum deposits in Pakistan are located in the Gilgit district of the autonomous region of Gilgit-Baltistan (formerly Northern Areas). The old ruby ​​deposits, discovered in the early 1970s, are in the Hunza valley , the younger ones are higher up in the mountains at an altitude of up to 5000 m. The individual sites such as "Ahmadabad", "Ali Abad", "Dorkhan" and "Ganesh" provide crystals up to 10 cm in size, mostly in a light red shade, which sit in a pure white marble.

Rubies and sapphires have been coming from the Afghan ruby deposit “Jegdalek” in the Sarobi district , Kabul province , since the 1870s. The deposit is located in a calcite-dolomite marble up to 2000 m thick and is worked over about 20 pits with more than 2000 opencast mines and digs.

Along with Sri Lanka, Myanmar is the classic mining area ("Upper Burma") for the noble corundum varieties. “The ruby ​​pits have been exploited since at least the 15th century; however, they were barely accessible to Europeans until the British took possession of them (1886). ”The most important area is Mogok in the Pyin U Lwin district in the Mandalay region . Rubies are extracted in Mogok in soaps along the rivers, in small pits or shafts or in larger trenches or opencast mines. In addition to the large number of rubies extracted, particularly large pieces are worth mentioning: the "Sun of Mogok" (1734 ct) found in 1993, the "Hixon Ruby" (196 ct, now in the Los Angeles County Museum of Natural History), the SLORC (504, 5 ct, property of the State of Myanmar) and a 3450 ct ruby ​​in the British Museum of Natural History in London.

Since the mining of ruby ​​began in 1991 at Möng Hsu in the Loilem District (Loilen District), Shan State, this discovery district has developed into one of the most important suppliers of gem quality ruby. An important feature of the ruby ​​crystals from Möng Hsu is their deep purple core (sapphire), which is surrounded by a ruby ​​red outer area. The violet core only changes to a deep red during heat treatment. In order to be able to bring this material onto the market, this heat treatment - often at high temperatures - has to be carried out on all stones from Möng Hsu.

The pink corundum and rubies discovered in Vietnam in 1987 near Lục Yên, Yên Bái province , and near Quỳ Châu, Nghệ An province , appeared two years later in Chanthaburi , Thailand , the world's most important transhipment point for raw corundum. The discovery area of ​​Lục Yên in the “Hoang Lien Son” mountain range in the Bắc-Bộ mountains provides, in addition to the better colored eluvial rubies from alluvion, also significantly larger corundums, which are often cloudy, but with appropriate cut give star rubies with clear rays. The rubies form crystals up to 12 cm in size, which can show shades of carmine red to pink to violet red.

Quỳ Châu not only supplies good rubies and star stones, but also stones with sharply separated color areas and attractive color combinations of blue / pink or blue / orange. Far away from here come milky or silky-cloudy pink-colored corundum, from which blue or almost red corundum is produced after heat treatment. Corundums with deep blue stripes are orange-pink after firing.

Ruby deposits in marble in the Turakuloma region in the Pamirs in Tajikistan have been known since the early 1980s . It is 6 km from the border with China and about 40 km northeast of Murghob (Murgab) in the autonomous province of Berg-Badachschan (Wilojati Muchtori Kuhistoni Badachschon). The richest and best known deposits among about 50 others are "Snezhnoe" or "Snejnaya", "Trika" and "Nadeschda" - they are located at an altitude of 3500 m. The light red, slightly violet-tinged crystals reach sizes up to 3 cm, rarely up to 6 cm.

Other Asian sites are in China , Indonesia , Israel , Japan , Kazakhstan , Cambodia , Kyrgyzstan , North and South Korea , Laos , Mongolia , Thailand , Turkey and the United Arab Emirates .

Africa

In Kenya , ruby deposits in the contact area of ​​small ultramafit intrusions in metasediments were discovered in the Mangari region, Taveta district , Taita-Taveta County , in the former Coast Province in Kenya. Rubies are found in idioblasts as crystals with a six-sided outline and as elongated, spindle-shaped crystals several centimeters in length and often with distinct color zones. The "Penny Lane Mine" supplies material of mostly cabochon quality, while the "John Saul Mine" occasionally provides excellent grinding material. Other sites can be found in the Taita Hills in the nearby Tsavo West National Park . Dusi (Garba Tula) in Isiolo County and Kitui County (Taawajah near Tsaikuri) 80 km east of Mount Kenya , all in the former Eastern Province , as well as the alluvial deposits on the Chania River and near Thika , both in Kiambu County , former Central Province , are further find points for ruby ​​and sapphire in Kenya.

"Longido", discovered at the beginning of the 20th century in the Arusha region in Tanzania, was the first economically interesting corundum deposit in Africa. Longido is a region with numerous individual deposits such as B. the "Muriatata Hills", the "Mundarara Mine" at Mdarara, at Lossogenoi and Naberera 70 km southeast of Arusha and at Malange in the Kiru Valley, about 180 km southwest of Longido. Here, too, there is idioblastic corundum, which can only rarely be sanded, in a green zoisite matrix with black pargasite crystals.

The valley of the Umba River in the Tanga region has been known for an enormous color spectrum of corundum since the middle of the 20th century. In 1969 stones with a weight of 100,000 ct are said to have been mined here every month. Faceted rubies up to 69 ct, faceted sapphires up to 40 ct and cabochons up to 90 ct were described.

There are also various deposits in the Morogoro region such as B. called the "Matombo" located 30 km southeast of Morogoro . Finally, the occurrence of Winza in the Mpwapwa district in the Dodoma region , located in amphibolites containing garnet, 115 km southeast of Dodoma and about 80 km from Mpwapwa , has to be mentioned, which provides corundum crystals in an impressive variety of crystal costumes.

• 

  “Munoanama”, Kilimanjaro Region , Tanzania

• 

  Winza, Dodoma Region, Tanzania

• 

  Madagascar

• 

  Ampanity District, Atsimo-Andrefana Region , Madagascar

• 

  Rodina farm area, Erongo , Namibia

• 

  Zimbabwe

• 

  Swaziland

• 

  Limpopo , South Africa

• 

  Soutspansberg, Limpopo, South Africa

Countless locations that supply corundum are known from Madagascar . The two most important are the sapphire deposits of "Andranondambo" near Maromby, Amboasary Sud , Anosy region (Fort Dauphin region), former province of Toliara , and several sites in the former province of Antsiranana (today region Diana ) , which were mined at the beginning of the 1990s . The latter include the “Ambondromifehy” sapphire deposit in the Antsiranana II district, as well as “Ambilobé”, “d'Anivoran” and “Milanoa”.

Finally, granulite facial pelites at Zazafotsy in the Ihosy district , Ihorombe region , former Fianarantsoa province , supply polychrome corundum crystals. The mining in the "Zazafotsy Quarry" (Amboarohy) began in 1989.

The rubies and sapphires found in Malawi on the plateau of Chimwadzulu Hill, Ntcheu district , up to 5 cm in size, have the highest light and birefringence observed on corundum. Corundum crystals from biotite schist in the farm area Harib 142, Karasburg-Ost , Region ǁKaras , Namibia , reach sizes of 12 × 4 cm. From the Rodina farm area (part of Graniet 67) east of the Spitzkoppe - Uis pad , Swakopmund , Erongo region , gray crystals up to 10 cm in length came from biotitic slate. In Zimbabwe , corundums were found in the “Somabula” region, 20 km southwest of Gweru , in the Midlands province , in fluvial Karoo-temporal conglomerates.

From Swaziland , corundums are known from alluvial and eluvial tin deposits along the Mbabane River near Mbabane and in the Ezulwini Valley, administrative region Hhohho , and from near Hlatikulu in the Shiselweni region. Among the large number of corundum sites in South Africa , only two sites from the former Northern Province or Transvaal Province , today Limpopo Province , should be highlighted. This concerns on the one hand Sudimani Spruit, Mopani district , where the world's largest corundum crystals were found (cf. above under “ Formation conditions ”) and, secondly, the “Palmietfontein 311 LS” farm in the Vhembe district, southwest of Louis Trichardt . From here mostly dull, dirty green crystals came, which in exceptional cases reached a weight of 15 kg and / or lengths of up to 15 cm. Also from “Waterside” north of the Soutpansberg (Salzpfannenberg), Vhembe district, and from the area of ​​the farms Barend 523 MS and Redhill 103 LS, also on Soutpansberg.

Other African sites are in Egypt , Burundi , the Democratic Republic of the Congo , Mozambique , Nigeria , Rwanda , Sierra Leone , and Somaliland .

America

Needle-like corundum crystal from an unnamed location in the San Jacinto Mountains - Santa Rosa and San Jacinto Mountains National Monument, Riverside County, California / USA

The best-known finding place for fine corundum in the United States is the sapphire deposit "Yogo Gulch", which is 95 km southeast of Great Falls on the eastern flank of the Little Belt Mountains in the gorge of the same name in the Yogo district, Little Belt Mountains in the Rocky Mountains , Judith Basin County , Montana . The first sapphire discovery in this area was on May 5, 1865.

In 1870, corundum was discovered in the Macon Co. southeast of Franklin , Ellijay District, Cowee Valley, North Carolina and was mined a year later by the Corundum Hill Mine / Culsagee Mine on Corundum Hill, one of the most important corundum deposits in the USA. The corundum crystals found here were "weighing up to over 300 pounds" and were colorless, banded in yellow, dark red, green, azure blue and white and blue. The largest crystal, opaque and with red and blue areas, weighed 141.5 kg, but was destroyed in a fire. Large crystals have also been found in Hogback Mountain in Jackson Co. and Buck Creek in Clay Co. , all North Carolina. Emery was mined in the Chester Emery Mines, Chester , Hampden County , Massachusetts . Other important corundum sites in the USA were the Cortland district in Westchester County , New York ; Franklin , Sussex Co. , New Jersey ; and the Laurel Creek Mine, Rabun Co. , Georgia .

From the "Unnamed Corundum Occurrences [2]", Soboba Hot Springs in the San Jacinto Mountains, Riverside County , California , spindle-shaped corundum crystals up to 12 inches (30.5 cm) in length are known. Even larger crystals, of which only fragments have survived, are said to have measured two feet (61 cm).

In Canada mainly from the province of Ontario , z. B. from the "Highland Corundum Occurrence" sitting in nepheline syenites, Cardiff Township in Haliburton County . Crystals up to 20 cm in size come from the “Gutz Corundum Occurrence”, Brudenell Township, located in syenite pegmatites, and from the “Craigmount workings” (Craigmont Mine), Raglan Township, both in Renfrew County in Ontario, located in nepheline-containing gneiss .

The first finds of ruby ​​and blue and purple sapphire in Brazil date from the 1930s. More than 30 mostly alluvial occurrences are currently known. “Lndaiá” not far from Vargem Alegre in Minas Gerais is the first commercially used deposit of corundum in grinding quality in Brazil and has been mining since 1994. In 1999 the extraction of grindable corundum began in Sapucaia, about 25 km south of Indaiá, and in 2000 corundum was discovered in Palmeira, 60 km southeast of Sapucaia. In the same state finds are found in the "Mina do Córrego do Fogo", Setubinha near Malacacheta, as well as at Campo Belo , Cláudio , Novo Cruzeiro , Conceição do Mato Dentro , Caputira , Datas, Passos and Bom Jesus da Penha .

In the state of Bahia there are the old deposits of Anage and Capim Grosso and the Lajedinho sites discovered in the more recent past near Vitória da Conquista , Catingal and Uauá.

The "Xerém" deposit near Duque de Caxias in the state of Rio de Janeiro produced high quality sapphires and corundum crystals weighing more than 2 kg in the 1960s. From the "Lavra do Escalvado" near Barra Velha , São João do ltaperiú, Santa Catarina , rubies and sapphires with asterism have been described.

Other locations in South and North America are in Argentina , Bolivia , Brazil , Chile , Greenland , Colombia , Mexico , Suriname and Uruguay .

Australia and New Zealand

In Australia , corundum comes mainly from the “Rubyvale”, “Sapphire” and “Scrub Lead Fossicking Area” in the “Anakie Field”, Central Highlands Region , Queensland , in the form of golden yellow, orange and green sapphires up to 70 ct and stones with asterism. Rough stones reach sizes of up to 1000 ct. The 1165 ct "Black Star of Queensland" was found in 1938 and ground into a cabochon of 733 ct.

In the area of ​​the “Lava Plains” locality, 100 km south of Mount Garnet, Kinrara National Park , Tablelands Region, Queensland , sapphires smell directly from a tertiary basalt chimney.

River gravel from the Weld River , Moorina, Blue Tier District, Break O'Day Municipality , Tasmania , has abundant sapphires in addition to zircon, topaz, chrysoberyl, spinel and cassiterite.

Hokitika in the Westland District , West Coast region on the South Island of New Zealand , is the location of an unusually colorful rock made of fuchsite, margarite, ruby ​​and sapphire as well as chromite and dravite , which is known as "goodletite" ( English ruby rock , ruby rock ) and as a gemstone is used. The exact location is glacial moraines and river deposits in a 20 × 20 km area from the Taipo River in the north to the Cropp River in the south. Goodletite was also found in the Whitcombe Valley and the Mont D'Or Mine, both at Ross , and on the Kaniere , Back Creek and Olderog Creek Rivers .

Corundum could also be detected in the Antarctic , in the dust of comet 81P / Wild 2 and in material from the moon .

Production countries and production rates

Russell Shor and Robert Weldon found that most of the production figures from individual deposits are notoriously implausible or at least difficult to interpret, even when they are figures from the mine owners or figures from official government agencies. So z. E.g. the delivery rates for the rough stones are given in kilograms (1 kg = 5,000  carats ) - without any further specifications on the quality of the material. Export figures, which rarely go into the different grades of gemstone, are often distorted to the financial advantage of the exporter and do not take into account the quantities illegally smuggled out of the respective country, which is a common practice in gem-producing countries.

Natural corundum is mined in a number of countries such as Myanmar, India, Thailand, Afghanistan, Cambodia , Sri Lanka and Vietnam, whereby in recent years corundum has also been mined in African countries such as Madagascar in the Kilimanjaro region in Tanzania. In the past a large part of the world's corundum production came from South Africa. Due to the production of artificial corundum, the production in South Africa (annual production 1980: 140 tons, 1990: less than 5 tons) is falling sharply.

The global world production for ruby ​​grew from approx. 5,000 kg in 1995 to about double (approx. 10,000 kg) in 2005. In 2002 the production figures fell sharply, but recovered from 2004 onwards. The significant increase in 2005 is due to the increased Ruby production in Kenya, Madagascar and Burma back. The production volumes for ruby ​​in the most important producing countries for the years between 1995 and 2005 are shown in the table opposite.

Annual production of the most important ruby ​​producing countries in kilograms

Producing country	1995	1996	1997	1998	1999	2000	2001	2002	2003	2004	2005
Afghanistan	70	70	70	90	70	70	55	55	55	30th
Australia				1		4th	7th	1	26th	2	27
Greenland										15th	30th
India	220	215	168	400
Kenya	1200	1200	5175	4001	4488	5896	5862	3043	2310	4758	5100
Madagascar	13	4th	19th	30th	6th	8th	941	889	800	741	920
Malawi	5	6th	20th	20th	15th		12		120	120	180
Myanmar	6th	566	1439	1476	1118	633	393	402	286	386	669
Pakistan	44	35	25th	15th	5	5	8th	21st	9	16	46
Nepal	150	150	150	150	150	150	150	150	150	150	150
Zimbabwe								18th
Tajikistan							5	5	5	5	5
Tanzania	3200	3200	3000	2000	1000	1070	1174	1800	2675	2800	2800
Thailand	20th	15th	20th	20th	25th	20th	20th	30th	15th	20th	20th
United States	15th	15th	15th	15th	15th	15th	15th	15th	15th	15th	15th
Vietnam	15th	40	70	70	70	70	70	70	70	30th	30th
total	4958	5516	10171	8288	6962	7941	8712	6499	6536	9088	9992

In contrast to ruby, world production of sapphire decreased from 1995 (26,900 kg) to 2005 (25,600 kg), although in 2000 even 32,500 kg of sapphire were mined. From 1995 to 1999 Australia was the most important producing country for sapphire, since 2000 Madagascar and Australia have alternated as the most important producing country for sapphire. The production volumes for sapphire in the most important producing countries for the years between 1995 and 2005 can be found in the adjacent table.

Annual production of the most important sapphire producing countries in kilograms

Producing country	1995	1996	1997	1998	1999	2000	2001	2002	2003	2004	2005
Afghanistan	400	400	400	500	400	400	300	300	300	155	155
Australia	13000	12000	11000	7500	7900	8700	8900	6600	5200	4800	5500
Ethiopia	10	10	10	10	10	10	10	10	10	10	1
People's Republic of China	500	750	1000	1300	1500	1700	2000	2300	2500	2700	3000
Greenland										10	21st
India					3	2	3	1	1	3	3
Cameroon	1000	1000	1000	1000	1000	1000	1000	1000	1000	1000	1000
Canada	10	1	4th	1						3	11
Kenya	2300	2300	2300	2300	2300	2300	2300	1200	900	2000	3500
Laos		2	654	1600	1600		106	167	461	142	140
Madagascar	115	160	4248	2547	3810	9536	8470	9326	6000	5890	4700
Malawi	10	15th	45	50	35		30th		280	280	280
Myanmar	20th	431	1083	1205	480	905	1212	463	583	388	699
Nepal	850	850	850	850	850	850	850	850	850	850	850
Sri Lanka	2700	2700	2700	3300	3300	3300	3300	4000	4000	4000	4000
Tanzania	4800	4800	4500	3500	2500	2531	3576	2400	1338	1400	1400
Thailand	170	110	150	160	200	150	170	260	110	150	150
United States	710	1200	1000	610	130	70	70	70	70	70	70
Vietnam	140	40	900	1700	1700	900	70	70	70	30th	30th
total	26855	26889	31964	28253	27838	32474	32487	29137	23793	23996	25595

Emery deposits also exist in the USA and Canada, but emery is only used in a few countries such as B. Greece and Turkey funded.

Large corundum

The compilation of the heaviest or largest known corundum crystals in the world comes for the most part from the book by Richard W. Hughes "Ruby & Sapphire".

description	Gross weight in kilograms	Dimensions in centimeters	Found year	Location	Owner / exhibition
red / blue crystal, opaque	141.5		before 1882	Franklin, North Carolina, USA	Shepard Collection, Amherst College, USA; destroyed by fire
sapphire	004.5		1928	Mogok, Myanmar	Storage unknown
hexagonal-bipyramidal crystal (not worth grinding)	152.0	68.58	1928	Leydsdorp, South Africa	Exhibited at the Geological Survey Museum, Pretoria, South Africa
Crystal with the shape of Sri Lanka	0 19.0			Sri Lanka	Exhibited at the American Museum of Natural History (?)
	015.42				Exhibited in the British Museum
pyramidal raw crystal, bluish gray (not worth grinding)	012.6	68.58 x 36.20 x 17.14	1967	Mogok, Myanmar	Myanma Gems Enterprise, Myanmar
dipyramidal crystal terminated on both sides	040.3			Rakwana, Sri Lanka	Storage unknown
bluish dipyramidal crystal (not worth grinding)	000.846		1990	Lokekhet, Mogok, Myanmar	Myanma Gems Enterprise, Myanmar
Ruby, proper name "Devil's Eye Ruby"	013.31			Myanmar (?)	Storage unknown
Corundum crystal		20.0 x 15.0		Craigmont Mine, Corundum Hill, Ontario, Canada	Royal Ontario Museum, Toronto

Corundum according to the Verneuil process

Synthetic corundum

Various synthetic corundums

Corundums have been produced synthetically since the end of the 19th century. In 1888, the Frenchman Auguste Verneuil (1856–1913) succeeded for the first time in producing artificial rubies from aluminum oxide and carefully selected additives using the so-called “melt-drop process” . This process was later called the Verneuil synthesis or Verneuil process in his honor .

The first production of electrical corundum took place in 1894 by the German chemist Ernst Moyat . Shortly before the First World War , Moyat received the imperial patent for the production of artificial corundum (normal corundum), which was reduced from the raw material bauxite in an electric arc furnace (electric melting - around 2120 ° C). Iron filings and coke were added to reduce the undesired accompanying substances . The result was a brown corundum (96% Al ₂ O ₃ ), ferrosilicon (FeSi, composition: ± 15% Si, 5% Al ₂ O ₃ , 3% TiO ₂ , 75% Fe, spec. 6.9 g / cm³, color silver gray).

As a result, so-called fine corundum was developed, with white corundum mainly being produced. The raw material is high-purity aluminum oxide (Al ₂ O ₃ ), the result of chemical cleaning of bauxite in the Bayer process and subsequent calcination, which produces red mud as a waste product in addition to aluminum oxide ( calcined alumina ) . The aluminum oxide is melted into white aluminum oxide in an electric arc furnace . The addition of 0.2% chromium (III) oxide creates pink corundum , with a 2% proportion so-called ruby corundum .

Another type of industrial production of corundum is hydrothermal crystal growth or the Czochralski process . However, this is only economical for single crystals. The majority of industrial corundum production worldwide is still carried out using the electro-melting process.

It is also noteworthy that this corundum can no longer be changed by the influence of acids or bases, apart from a melt of NaOH; they can only be liquefied again at a temperature of around 2,050 ° C.

use

Corundum in its natural form is now almost exclusively used as a gemstone. For technical applications, for which it is suitable due to its properties, almost exclusively synthetic corundum is used.

As a gem

Finger ring with faceted sapphire

A number of well-known jewelery and precious stones are created from the actually colorless aluminum oxide due to impurities . The red stones contain chromium ions and are traditionally called rubies , all others are called sapphires in a broader sense , but in a narrower sense this name only refers to the blue variants, the colors of which are created by adding iron , titanium and vanadium ions.

A special effect that sometimes shows up in corundum is what is known as asterism . In contrast to the cat's eye effect, in which the fibers that trigger the effect are embedded in parallel, the direction of the fibers in asterism is determined by the symmetry of the host crystal at 120 ° angles. A six-pointed star is formed from bright light, which, depending on the angle of view, is created by reflection on microscopic, needle-like, fibrous rutile crystals. In order to work it out particularly succinctly, the spherical to egg-shaped cut of the cabochon (Mugelschliff) is often chosen for this corundum . Other effects caused by the presence of rutile needles can be silk gloss (only a small number of embedded fibers) or chatoyance (cat's eye effect, when the rutile fibers are embedded in parallel).

Corundum used as a gem is often treated. With this treatment, cracks and voids heal, whereas with high-temperature treatment the transparency and the color are improved. Cracks close to the surface are removed with wax or with silicate glass, whereby the stone to be treated is immersed in a silicate melt or heated together with a powdery filler such as borax or glass. At high temperatures the filling material melts and gets into the cracks, fissures and cavities. Blue sapphires can be produced from white sapphire by diffusion treatment, but the blue layer is only very thin and only close to the surface. However, these diffusion-treated stones can be recognized relatively easily by immersing them in methylene iodide with simultaneous diffuse fluoroscopy. Aids in recognition are the larger relief at the contact of facets as a result of color concentrations, the mottling of the color caused by diffusion and the characteristic colorless areas.

In technology

granular electro corundum for industrial purposes

Synthetic corundum is used industrially and in the tool sector because of its high hardness as an abrasive (on sandpaper , in the form of cutting discs , but also in polishes ). Corundum is also used as a blasting medium for sandblasting , since normal sand can cause the lung disease silicosis . Corundum is also used as an aggregate for hard concrete (e.g. as a filler for the walls of safes .)

As alumina (calcined clay), aluminum oxide ceramics are used in electrical engineering (see also the article aluminum oxide ). Because of its low dielectric loss factor, it is used as a dielectric and to implement striplines and capacitors in high-frequency technology. Aluminum oxide ceramic plates serve as electronics substrates for thick-film technology , for thin-film technology and for platinum temperature measuring resistors . Due to the fact that these ceramics can be easily metallized, electronic components such as resistors or LEDs can also be soldered on directly, with the ceramic simultaneously functioning as a heat sink . In technical ceramics , the hard, abrasion-resistant and corrosion-resistant aluminum oxide ceramic is used, for. B. in the form of sinks, hotel dishes and bulletproof clothing and as a material for burner tubes of high-pressure gas discharge lamps or as an additive , z. B. for non-slip ceramic tiles and as a non-slip deck coating for frigates of the German Navy.

Very finely ground corundum (grain size about 100 nm) is used to produce scratch-resistant paints. In order to maintain the transparency of the lacquer, each grain is silanized . The different abrasion classes of laminate floors are also based on different amounts of added silanized corundum in the lacquer layer.

Another large area of ​​application of the industrially produced white aluminum oxide results from its high temperature resistance (melting point 2050 ° C), but also due to its high chemical resistance. Corundum in grain fractions of 0–6 mm is used as the main component and as an aggregate for the production of refractory materials, for the production of refractory linings for blast furnaces or for the production of metal casting molds .

Ruby as a watch bearing

Due to its hardness and abrasion resistance, corundum is well suited as a bearing in watches and precision devices and as a counter bearing when using micrometer screws , for example in mirror holders. The same properties allow it to be used in the composite material of the scraper for snow plows .

The titanium: sapphire laser (Ti: Sa laser) , which was first described in 1982, has a titanium-doped corundum crystal as its active medium, while the historically interesting ruby laser has a chromium-doped corundum crystal ( ruby ). Ti: Sa lasers have almost completely displaced the dye lasers and now dominate the areas for tunable lasers and the generation of ultra-short laser pulses .

Commercial blue light-emitting diodes consist in most cases of gallium nitride , which was epitaxially deposited on synthetic corundum. Pure corundum is used as sapphire glass in clocks ( watch glass or back wall) and rarely as a display cover in digital cameras (see Leica M 8 and M9-P). For vacuum technology applications in vacuum optics, sapphire glass is used as a sight glass for viewing the inside of vacuum chambers. Corundum is often used instead of diamond as a stylus material in the pickups of turntables, which led to the colloquial term “sapphire” for the stylus.

See also

• Systematics of the minerals
• List of minerals
• List of mineral jewelry and precious stones

literature

• Corundum . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America . 2001 ( handbookofmineralogy.org [PDF; 71 kB ; accessed on March 6, 2018]).
• Hans Jürgen Rösler : Textbook of Mineralogy . 4th revised and expanded edition. German publishing house for basic industry (VEB), Leipzig 1987, ISBN 3-342-00288-3 , p. 378-379 .
• Friedrich Klockmann : Klockmann's textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp. 512-513 (first edition: 1891).
• Petr Korbel, Milan Novák: Encyclopedia of Minerals . Dörfler Verlag GmbH, Eggolsheim 2002, ISBN 3-89555-076-0 , p. 82 .
• Walter Schumann: Precious stones and gemstones. All kinds and varieties. 1900 unique pieces . 16th revised edition. BLV Verlag, Munich 2014, ISBN 978-3-8354-1171-5 , pp. 98; 269 (corundum group; synthetic manufacture of precious and semi-precious stones).
• Dietmar Schwarz, Susanne Greiff, Roland Schlüssel, Karl Schmetzer, Adolf Peretti, Heinz-Jürgen Bernhardt, Paul Rustenmeyer, George Bosshart, Robert E. Kane, Andreas Weerth, Christopher P. Smith, Chico Bank, Jan Kanis, Barry J. Neville, Friedrich v. Gnielinski, Rupert Hochleitner, Henry H. Hänni: Rubin, Saphir, Korund. Beautiful, hard, rare, precious (= Christian Weise [Hrsg.]: ExtraLapis . Band 15 ). Christian Weise Verlag, 2002, ISBN 3-921656-45-1 , ISSN  0945-8492 , p. 1-96 .
• Richard W. Hughes: Ruby & Sapphire . RWH Publishing, Boulder, CO 1997, OCLC 768295509 , pp. 1-512 .
• JF Halford-Watkins: The Book of Ruby & Sapphire (From an Unpublished 1934 Manuscript) . Ed .: Richard W. Hughes. RWH Publishing, Boulder, CO 2012, ISBN 978-0-9645097-0-2 , pp. 1-434 ( ruby-sapphire.com [accessed March 27, 2018]).

Web links

Commons : Corundum  - collection of images, videos and audio files

• Mineral Atlas: Corundum (Wiki)
• Corundum. In: mindat.org. Hudson Institute of Mineralogy, accessed June 6, 2020 . 
• David Barthelmy: Corundum Mineral Data. In: webmineral.com. Retrieved June 6, 2020 . 
• Corundum search results. In: rruff.info. Database of Raman spectroscopy, X-ray diffraction and chemistry of minerals (RRUFF), accessed June 6, 2020 . 
• American-Mineralogist-Crystal-Structure-Database - Corundum. In: rruff.geo.arizona.edu. Retrieved June 6, 2020 . 
• Gemstone etiquette from Prof. Leopold Rössler - Corundum. In: beyars.com. Retrieved June 6, 2020 . 

Individual evidence

1. ↑ Stefan Weiß: The large Lapis mineral directory. All minerals from A - Z and their properties. Status 03/2018 . 7th, completely revised and supplemented edition. Weise, Munich 2018, ISBN 978-3-921656-83-9 .
2. ^ ^{A b c d} Charles Greville: On the Corundum Stone from Asia . In: Philosophical Transactions of the Royal Society of London . tape 1798 , Part II, 1798, pp. 403-448 ( available online in Philosophical Transactions , p. 403 in Google Book Search).
3. ^ ^{A b} Charles Greville: About the corundum from Asia by Mr. Charles Greville (translated from English and accompanied by comments by Mr. SWA Herder) . In: Neues Bergmännisches Journal . tape III , 1802, pp. 90–208 ( available online in Neues Bergmännisches Journal , p. 90 in the Google book search).
4. ↑ ^{a b} Martin Heinrich Klaproth : Chemical experiments on the Demanthspath . In: Martin Heinrich Klaproth (Ed.): Contributions to the chemical knowledge of mineral bodies . tape  1 . Decker & Compagnie and Heinrich August Rottmann, Posen and Berlin 1795, p. 47–80 , urn : nbn: de: bvb: 12-bsb10073069-3 ( available online in Articles on the chemical knowledge of mineral bodies , p. 47 ff. In the Google book search).
5. ↑ ^{a b} Franz Ambrosius Reuss : Textbook of Mineralogy based on Mr. OBR Karsten's mineralogical tables . Friedrich Gotthold Jacobäer, Leipzig 1802, p.  16 ( available online in Textbook of Mineralogy , p. 16 ff. In the Google book search).
6. ↑ ^{a b} Cajus Plinius Secundus : Natural history thirty-seventh book . XV. Six kinds of diamond. In: Max Ernst Dietrich Lebrecht Strack (Ed.): Natural history . Heinrich Strack, Bremen 1856, p.  541–542 ( available online in Natural History Book 37 , pp. 541–542 in the Google book search - Latin: Naturalis historia . Translated by Christian Friedrich Lebrecht Strack, first edition: 0077).
7. ↑ ^{a b c d e f g h i j k l m} Hugo Strunz , Ernest H. Nickel : Strunz Mineralogical Tables . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p.  192-193 .
8. ↑ ^{a b c d e f g h i j k l} Carl Hintze : Handbuch der Mineralogie. First volume. Second division: oxides and haloids . Veit & Co., Leipzig 1915, p.  1739-1782 .
9. ↑ ^{a b} Cajus Plinius Secundus : Natural history thirty-sixth book . XV. Six kinds of diamond. In: Max Ernst Dietrich Lebrecht Strack (Ed.): Natural history . Heinrich Strack, Bremen 1856, p.  541–542 ( available online in Natural History Book 37 , pp. 541–542 in the Google book search - Latin: Naturalis historia . Translated by Christian Friedrich Lebrecht Strack, first edition: 0077).
10. ^ ^{A b} Christian August Siegfried Hoffmann : Handbook of Mineralogy: First Volume . Craz & Gerlach, Freiberg 1811, p.  547-577 ( available online in Handbuch der Mineralogie , pp. 547 ff. In the Google book search).
11. ↑ ^{a b} Pedanios Dioskurides : Des Pedanios Dioskurides from Anazarbos medicament theory in five books . tape  5 . Ferdinand Enke, Stuttgart 1902, 165 (166), pp. 553 ( buecher.heilpflanze-welt.de [accessed on March 10, 2018] Smirgel).
12. ↑ ^{a b} Nikolai von Kokscharow : materials for mineralogy Russia . First volume. tape  1 . Carl Kray, St.-Petersburg 1853, p. 30 ( available online in materials on the mineralogy of Russia, vol. I , p. 30 in the Google book search).
13. ↑ ^{a b} Nikolai von Kokscharow : materials for mineralogy Russia . Second volume. tape  2 . Alexander Jacobson, St. Petersburg 1854, p. 80 ( available online in materials on the mineralogy of Russia, Vol. II , p. 80 in the Google book search).
14. ^ ^{A b} René-Just Haüy : Textbook of Mineralogy, elaborated by the citizen Haüy . Third part, plus the third booklet of the copper plates. tape  3 . CH Reclam, Paris and Leipzig 1806, p. 1–18 ( available online in Textbook of Mineralogy , p. 1 in the Google book search).
15. ↑ ^{a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac} Corundum . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America . 2001 ( handbookofmineralogy.org [PDF; 71  kB ; accessed on March 6, 2018]).
16. ↑ ^{a b c d e f} Dietmar Schwarz, Susanne Greiff, Roland Schlüssel, Karl Schmetzer, Adolf Peretti, Heinz-Jürgen Bernhardt, Paul Rustemeyer, George Bosshart, Robert E. Kane, Andreas Weerth, Christopher P. Smith, Chico Bank, Jan Kanis, Barry J. Neville, Friedrich v. Gnielinski, Rupert Hochleitner, Henry H. Hänni: Corundum at a glance . In: ruby, sapphire, corundum. Beautiful, hard, rare, precious (= Christian Weise [Hrsg.]: ExtraLapis . Band 15 ). Christian Weise Verlag, 1998, ISBN 3-921656-45-1 , ISSN  0945-8492 , p. 3 .
17. ↑ See the entry [www.oed.com/view/Entry/42124 "corundum, n."] In OED Online, Oxford University Press. Date of access: November 13, 2018.
18. ^ John Woodward : A catalog of the foreign fossils in the collection of J. Woodward MD Brought as well from several Parts of Asia, Africa, and America; as from Sweden, Germany, Hungary, and other Parts of Europe. Part I Reclam, Paris and Leipzig 1719, p.  6 (English, archive.org [PDF; 32.0 MB ; retrieved on November 7, 2018] Bundle of various works; P. 514 in the entire bundle).
19. ^ John Woodward : An Addition to the Catalog of the Foreign Native Fossils In the Collection of J. Woodward MD CH Reclam, Paris and Leipzig 1725, p.  6 (English, archive.org [PDF; 32.0 MB ; retrieved on November 7, 2018] Bundle of various works; P. 610 in the entire bundle).
20. ^ Richard Kirwan : Elements of mineralogy . Second edition with considerable improvements and additions. J. Nichols, London 1794, p.  335 ( available online in Elements of mineralogy , p. 335 in the Google book search).
21. ^ Martin Heinrich Klaproth : Recherches chimiques sur le Spath adamantin . In: Mémoires de L'Académie Royale des Sciences et Belles-Lettres Aout 1786 jusqu'a la fin de 1787 . tape  1786/87 , 1792, pp. 148–159 ( available online in treatises of the Royal Prussian Academy of Sciences , p. 148 in the Google book search).
22. ↑ Martin Heinrich Klaproth : Investigation of the oriental sapphire . In: Martin Heinrich Klaproth (Ed.): Contributions to the chemical knowledge of mineral bodies . tape  1 . Decker & Compagnie and Heinrich August Rottmann, Posen and Berlin 1795, p. 81–89 , urn : nbn: de: bvb: 12-bsb10073069-3 ( available online in Articles on the chemical knowledge of mineral bodies , p. 81 ff. In the Google book search).
23. ^ Jacques Louis de Bournon : Description of the Corundum Stone, and its Varieties, commonly known by the Names of Oriental Ruby, Sapphire, & c .; with observations on some other mineral substances . In: Philosophical Transactions of the Royal Society of London . tape  1802 , Part II, 1802, pp. 233–326 ( available online in Philosophical Transactions , p. 234 in the Google book search).
24. ↑ Dietrich Ludwig Gustav Karsten : Mineralogical tables: elaborated with consideration of the latest discoveries and provided with explanatory notes . Second improved and enlarged edition. Heinrich August Rottmann, Berlin 1808, p.  46 ( available online in treatises of the Royal Prussian Academy of Sciences , p. 46 in the Google book search - first edition: 1800, class I: earth and stone species, order 5: the alum earth genus Corund, species: 1. Common Corund and 2 . Diamantspath).
25. ^ Johann Friedrich Ludwig Hausmann : Handbook of Mineralogy . Second volume, from the class of the incombustibilien containing the subordination of the earths. tape  2 . Vandenhoeck & Ruprecht, Göttingen 1813, p. 366–367 ( available online in Handbuch der Mineralogie , pp. 366–367 in the Google book search).
26. ↑ ^{a b c d e f g} Helmut Schrätze , Karl-Ludwig Weiner : Mineralogie. A textbook on a systematic basis . de Gruyter, Berlin; New York 1981, ISBN 3-11-006823-0 , pp.  390-393 (corundum).
27. ↑ ^{a b c d e f g h i j k l m n o p q} Friedrich Klockmann : Klockmann's textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp.  512-513 (first edition: 1891).
28. ↑ ^{a b c d e f g h i j k l m n o p q r s t u} Corundum at mindat.org (English)
29. ↑ ^{a b c d e f g h i j k l m} Charles Palache , Harry Berman , Clifford Frondel : Corundum. [Al ₂ O ₃ ] . In: The System of Mineralogy of James Dwight Dana and Edward Salisbury Dana: Yale University 1837-1892 . Elementes, sulfides, sulfosalts, oxides. 7th edition. tape  I . John Wiley and Sons, New York, London, Sydney 1944, ISBN 0-471-19272-4 , pp. 520-527 (English).
30. ↑ ^{a b} University of Freiburg - corundum structure
31. ↑ ^{a b c d e f g h i} Hans Jürgen Rösler : Textbook of Mineralogy . 4th revised and expanded edition. German publishing house for basic industry (VEB), Leipzig 1987, ISBN 3-342-00288-3 , p.  378-379 .
32. ↑ ^{a b} Rupert Hochleitner, Henning von Philipsborn, Karl Ludwig Weiner: Minerals: Determining according to external characteristics . 3. Edition. E. Schweizerbart'sche Verlagsbuchhandlung, Stuttgart 1996, ISBN 3-510-65164-2 , p. 352-353 .
33. ^ ^{A b c} Christopher P. Smith: Rubies and pink sapphires from the Pamir Mountain Range in Tajikistan, former USSR . In: The Journal of Gemmology . tape 26 , no. 2 , 1998, p. 103-561 , doi : 10.15506 / JoG.1998.26.2.103 ( gem-a.com [PDF; 6.2 MB ; accessed on March 15, 2018]).
34. ↑ Fancy Colored Sapphires: The Beauty beyond “Blue” of Sapphire and “Red” of Ruby. (PDF 1514 kB) In: ssef.ch. Retrieved June 6, 2020 .  
35. ^ W. William Hanneman: Pragmatic Spectroscopy For Gemologists . 1st edition. Hanneman Gemological Instruments, Unknown 2011, pp. 1-59 .
36. ^ ^{A b c} Walter Schumann: Precious stones and gemstones. All kinds and varieties. 1900 unique pieces . 16th revised edition. BLV Verlag, Munich 2014, ISBN 978-3-8354-1171-5 , pp. 98; 269 (corundum group; synthetic manufacture of precious and semi-precious stones).
37. ↑ Hans Pichler, Cornelia Schmitt-Riegraf: Rock -forming minerals in thin sections . 1st edition. Enke, Stuttgart 1987, ISBN 3-432-95521-9 , pp. 71 .
38. ↑ ^{a b c d} University of Texas at Austin - Corundum. In: geo.utexas.edu. September 14, 2017, accessed June 6, 2020 .  
39. ↑ ^{a b} Mineralienatlas - Korund
40. ↑ Cornelio August Doelter , Hans Leitmeier : Handbuch der Mineralchemie . Volume III Second half contains: Li, Na, K, Cu, Rb, Ag, Cs, Au, Be, Mg, Ca, Zn, Sr, Cd, Ba, Hg, Ra, B, Al, Ga, In, Tl, Rare earth metals, Fe, Mn, Co, Ni and platinum metals. Ed .: Cornelio August Doelter, Hans Leitmeier. tape  1 . Springer, Berlin, Heidelberg 1926, ISBN 978-3-642-49539-7 , pp. 436–462 , doi : 10.1007 / 978-3-642-49830-5 ( available online in Handbuch der Mineralchemie , p. 441 in the Google book search).
41. ↑ oskar-moser.de - Technical data synthetic sapphire
42. ^ ^{A b} Richard W. Hughes: The rubies and spinels of Afghanistan: A brief history . In: The Journal of Gemmology . tape 24 , no. 4 , 1994, pp. 256–267 ( gem-a.com [PDF; 5.6 MB ; accessed on June 6, 2020]).
43. ↑ Deltalumite at mindat.org (English)
44. ↑ Ch. Siegert, AL Shirokov, LV Nikishova, LA Pavlova, OA Babiy: Natural analogues of the alumina modifications (θ-Al ₂ O ₃ , and δ-Al ₂ O ₃ ) in permafrost area sediments . In: Doklady Akad. Nauk SSSR . tape 313 , 1990, pp. 689-692 (Russian).
45. ↑ ^{a b c} Jolyon and Katya Ralph: Corundum. In: gemdat.org. Retrieved June 6, 2020 .  
46. ↑ ^{a b c d e} Max Bauer: Gemstone customer. A generally understandable description of the properties, the occurrence and the use of the gemstones, together with instructions for determining the same for mineralogists, stone cutters, jewelers, etc. 1st edition. Tauchnitz, Leipzig 1896, p. 1-711 .
47. ↑ Dr. Pohlig: About chlorosapphire, a green corundum . In: Meeting reports Niederrheinische Gesellschaft Bonn from May 7th and July 9th 1888 . tape 44 , 1888, pp. 61 .
48. ↑ Anselmus de Boodt : Gemmarum et Lapidum Historia . qua non solum ortius, vis et precium, sedetiam modus quo exiis, olea, salia, tincturae, essentiae, arcana et magisteria artechymica confici poßint: ostenditur opus principibus, medicis, chymicis, physicis, ac liberalioribus ingeniis utiliss. ; cum variis figuris, indiceque duplici et copioso. Andreas Wechel Erben, Claude de Marne, Johann Aubry Erbe, Hanoviae (Hanau) 1609, p.  111–112 (Latin, available online in Gemmarum et Lapidum Historia , p. 111 in the Google book search).
49. ^ Karl Schmetzer, Henry H. Hänni, Heinz-Jürgen Bernhardt, Dietmar Schwarz: Trapiche rubies . In: Gems & Gemology . tape XXXII , no. 4 , 1996, pp. 242–250 ( gia.edu [PDF; 901 kB ; accessed on March 7, 2018]).
50. ^ Karl Schmetzer, Heinz-Jürgen Bernhardt: Trapiche rubies from Southeast Asia . In: ruby, sapphire, corundum. Beautiful, hard, rare, precious (= Christian Weise [Hrsg.]: ExtraLapis . Band 15 ). Christian Weise Verlag, 1998, ISBN 3-921656-45-1 , ISSN  0945-8492 , p. 30-33 .
51. ↑ Ichiro Sunagawa: Growth histories of mineral crystals as seen from their morphological features . In: Kullaiah Byrappa, Tadashi Ohachi (Ed.): Crystal Growth Technology (=  Springer series in materials processing ). William Andrew Publ., Springer Verlag, Norwich, Berlin-Heidelberg 2003, ISBN 3-540-00367-3 , pp. 18–21 ( available online in Crystal Growth Technology , pp. 18–21 in Google Book Search).
52. ↑ ^{a b} Goodletite. In: mindat.org. Hudson Institute of Mineralogy, accessed June 6, 2020 .  
53. ↑ Mindat - Number of localities for corundum (English)
54. ↑ ^{a b c d e f} List of localities for corundum in the Mineralienatlas and Mindat , accessed on June 6, 2020.
55. ^ ^{A b c} Bruce Cairncross, Roger Dixon: Minerals of South Africa . 2nd Edition. Geological Society of South Africa, Linden (South Africa) 1999, ISBN 0-620-19324-7 , pp. 24-26 .
56. ↑ Ambrogio Rovetti, Ilaria Rovetti, Marco Pacciorini: Campolungo, Switzerland: New discovery of the largest corundum crystals in the Alps . In: Lapis . tape 19 , no. 9 , 1994, pp. 35-40 .
57. ^ Rupert Hochleitner: Europe: Corundum for collecting . In: ruby, sapphire, corundum. Beautiful, hard, rare, precious (= Christian Weise [Hrsg.]: ExtraLapis . Band 15 ). Christian Weise Verlag, 1998, ISBN 3-921656-45-1 , ISSN  0945-8492 , p. 80-85 .
58. ↑ Dietmar Schwarz: India, land of large rubies? In: ruby, sapphire, corundum. Beautiful, hard, rare, precious (= Christian Weise [Hrsg.]: ExtraLapis . Band 15 ). Christian Weise Verlag, 1998, ISBN 3-921656-45-1 , ISSN  0945-8492 , p. 14-15 .
59. ↑ Robert E. Kane: Kashmir: the new rubies . In: ruby, sapphire, corundum. Beautiful, hard, rare, precious (= Christian Weise [Hrsg.]: ExtraLapis . Band 15 ). Christian Weise Verlag, 1998, ISBN 3-921656-45-1 , ISSN  0945-8492 , p. 40-43 .
60. ↑ Dietmar Schwarz: The first classic: Sri Lanka . In: ruby, sapphire, corundum. Beautiful, hard, rare, precious (= Christian Weise [Hrsg.]: ExtraLapis . Band 15 ). Christian Weise Verlag, 1998, ISBN 3-921656-45-1 , ISSN  0945-8492 , p. 16-17 .
61. ^ John I. Koivula, Robert C. Kammerling: Gem News: Huge, doubly-terminated sapphire crystal . In: Gems & Gemology . tape 25 , no. 4 , 1989, pp. 247 ( gia.edu [PDF; 4.1 MB ; accessed on March 15, 2018]).
62. ^ Dietmar Schwarz: Nepal: Ganesh Himal . In: ruby, sapphire, corundum. Beautiful, hard, rare, precious (= Christian Weise [Hrsg.]: ExtraLapis . Band 15 ). Christian Weise Verlag, 1998, ISBN 3-921656-45-1 , ISSN  0945-8492 , p. 50-51 .
63. ^ Roland Keys: Mogok, Myanmar. A journey through Burma to the most beautiful rubies and sapphires in the world . 1st edition. Christian Weise Verlag, Munich 2002, ISBN 3-921656-60-5 , p. 224-235 .
64. ^ Eduard Gübelin: The Ruby Mines in Mogok in Burma . In: The Journal of Gemmology . tape 9 , no. 12 , 1965, p. 411-425 ( gem-a.com [PDF; 3.0 MB ; accessed on June 6, 2020]).
65. ^ Robert C. Kammerling, Kenneth Scarratt, George Bosshart, E. Alan Jobbins, Robert E. Kane, Edward J. Gübelin, Alfred A. Levinson: Myanmar * and its gems - an update . In: The Journal of Gemmology . tape 24 , no. 1 , 1994, p. 3–40 ( gem-a.com [PDF; 5.0 MB ; accessed on March 15, 2018]).
66. ^ Richard W. Hughes, U Hla Win: Burmese sapphire giants . In: The Journal of Gemology . tape 24 , no. 8 , 1995, p. 551–561 ( gem-a.com [PDF; 23.5 MB ; accessed on March 15, 2018]).
67. ↑ George R. Rossman: The Geochemistry of Gems and its relevance to gemology: different traces, different prices . In: Elements . tape 5 , no. 3 , 2009, p. 159-162 , doi : 10.2113 / gselements.5.3.159 .
68. ↑ ^{a b c} George Bosshart: Vietnams Korunde im Handel . In: ruby, sapphire, corundum. Beautiful, hard, rare, precious (= Christian Weise [Hrsg.]: ExtraLapis . Band 15 ). Christian Weise Verlag, 1998, ISBN 3-921656-45-1 , ISSN  0945-8492 , p. 39 .
69. ^ Paul Rustemeyer: Luc Yen, North Vietnam . In: ruby, sapphire, corundum. Beautiful, hard, rare, precious (= Christian Weise [Hrsg.]: ExtraLapis . Band 15 ). Christian Weise Verlag, 1998, ISBN 3-921656-45-1 , ISSN  0945-8492 , p. 34-38 .
70. ↑ Le Thi-Thu Huong: Gem Notes Large Ruby Matrix Specimen from Lục Yên, Vietnam . In: The Journal of Gemmology . tape 35 , no. 4 , 2016, p. 284-285 .
71. ↑ Pham Van Long, Vincent Pardieu, Gaston Giuliani: Update on Gemstone Mining in Luc Yen, Vietnam . In: Gems & Gemology . tape 49 , no. 4 , 2013, p. 233-245 , doi : 10.5741 / GEMS.49.4.233 .
72. ↑ Ulrich Henn, H. Bank, M. Bank-Scherner: Rubies from the Pamir Mountains, USSR . In: Journal of the German Gemological Society . tape 39 , no. 4 , 1990, pp. 201-204 .
73. ↑ Elena S. Sorokina, Andrey K. Litvinenko, Wolfgang Hofmeister, Tobias Häger, Dorrit E. Jacob, Zamoniddin Z. Nasriddinov: Rubies and sapphires from Snezhnoe, Tajikistan . In: Gems & Gemology . tape 51 , no. 160–175 , 2015, pp. 247 , doi : 10.5741 / GEMS.51.2.160 ( gia.edu [PDF; 5.3 MB ; accessed on March 15, 2018]).
74. ↑ Dietmar Schwarz: Rubies and sapphires from Africa . In: ruby, sapphire, corundum. Beautiful, hard, rare, precious (= Christian Weise [Hrsg.]: ExtraLapis . Band 15 ). Christian Weise Verlag, 1998, ISBN 3-921656-45-1 , ISSN  0945-8492 , p. 52-53 .
75. ↑ ^{a b c} Dietmar Schwarz: Tanzania . In: ruby, sapphire, corundum. Beautiful, hard, rare, precious (= Christian Weise [Hrsg.]: ExtraLapis . Band 15 ). Christian Weise Verlag, 1998, ISBN 3-921656-45-1 , ISSN  0945-8492 , p. 54-55 .
76. ^ Karl Schmetzer, Werner Radl, Dietmar Schwarz: Winza a new ruby ​​deposit in Tanzania . In: Lapis . tape 34 , no. 5 , 2009, p. 41-46 .
77. ↑ Dietmar Schwarz, Jan Kanis: Madagascar: Sapphires from the South and Since '95: Sapphires from the North . In: ruby, sapphire, corundum. Beautiful, hard, rare, precious (= Christian Weise [Hrsg.]: ExtraLapis . Band 15 ). Christian Weise Verlag, 1998, ISBN 3-921656-45-1 , ISSN  0945-8492 , p. 60-63 .
78. ^ Ludi von Bezin, Rainer Bode, Steffen Jahn: Namibia: Minerals and Localities II . 1st edition. Bode, Salzhemmendorf 2016, ISBN 978-3-942588-19-5 , p. 160 .
79. ^ Joseph Hyde Pratt: Corundum and its occurrence and distribution in the United Staates (a revised and enlarged edition of Bulletin 180) . In: USGS Bulletin . tape 269 , 1906, pp. 111–115 ( available online in USGS Bulletin 269 , pp. 111 ff. In Google Book Search).
80. ↑ Robert E. Kane: The Sapphires of Montana . In: ruby, sapphire, corundum. Beautiful, hard, rare, precious (= Christian Weise [Hrsg.]: ExtraLapis . Band 15 ). Christian Weise Verlag, 1998, ISBN 3-921656-45-1 , ISSN  0945-8492 , p. 64-67 .
81. ↑ Robert J. Schabilion: Down the Crabtree: A historical review of north Carolina mining and mines . AuthorHouse, Bloomington, Indiana 2009, ISBN 978-1-4490-5124-2 , pp. 154 ( available online in Down the Crabtree , pp. 154 ff. In the Google book search).
82. ^ Mindat - "Unnamed Corundum Occurrences [2]" at Soboba Hot Springs, California
83. ^ ^{A b} Ann P. Sabina: Rocks and minerals for the collector: Ottawa to North Bay and Huntsville, Ontario; Gatineau (Hull) to Waltham and Témiscaming, Quebec (Miscellaneous Report 48) . Geological Survey of Canada, Ottawa 2007, ISBN 0-660-19556-9 , pp. 55–62 ( gc.ca [PDF; 32.8 MB ; accessed on November 12, 2017]).
84. ↑ Barry J. Neville, Friedrich v. Gnielinski: Australia's sapphire deposits . In: ruby, sapphire, corundum. Beautiful, hard, rare, precious (= Christian Weise [Hrsg.]: ExtraLapis . Band 15 ). Christian Weise Verlag, 1998, ISBN 3-921656-45-1 , ISSN  0945-8492 , p. 70-75 .
85. ^ Russell Shor, Robert Weldon: Ruby and Sapphire production and distribution: a quarter century of change . In: Gems & Gemology . tape 45 , no. 4 , 2009, p. 236-259 ( gia.edu [PDF; 3.1 MB ; accessed on November 9, 2018]).
86. ^ Corundum. In: futuremarketinsights.com. Retrieved June 6, 2020 .  
87. ↑ Patrick Maseko: mineral abrasives in South Africa 2007 Directorates: Mineral Economics: Report R64 / 2007 . 2007, p. 3–6 (English, gov.za [PDF; 604 kB ; accessed on November 10, 2018]).
88. ↑ ^{a b c d} Thomas R. Yager, W. David Menzie, Donald W. Olson: Weight of production of emeralds, rubies, sapphires, and tanzanite from 1995 through 2005: US Geological Survey Open-File Report 2008-1013 . 2008, p. 1–9 (English, usgs.gov [PDF; 48 kB ; accessed on November 10, 2018]).
89. ↑ Jessica Elzea Kogel, Nikhil C. Trivedi, James M. Barker, Stanley T. Krukowski (Eds.): Industrial Minerals & Rocks: Commodities, Markets, and Uses . 7th edition. Society for Mining, Metallurgy, and Exploration, Inc., Littleton / Colorado 2006, ISBN 978-0-87335-233-8 , pp. 22 (English, available online in Industrial Minerals & Rocks: Commodities, Markets, and Uses , p. 22 in the Google book search).
90. ^ Richard W. Hughes: Ruby & Sapphire . RWH Publishing, Boulder, CO 1997, OCLC 768295509 , pp. 1-512 ( Ruby & Sapphire. Table 10.9: Summary of rough corundum giants ( Memento of November 5, 2019 in the Internet Archive )).
91. ↑ Dieko Hillebrands Bruins, Hans-Jürgen Dräger: tools and machine tools for metal cutting: T. 1: Zerspanungslehre, Getriebelehre, components, equipment . 5th revised and expanded edition. Carl Hanser Verlag, Munich 1968, p. 236 .
92. Jump up ↑ Robert E. Kane, Robert C. Kammerling, John I. Koivula, James E. Shigley, Emmanuel Fritsch: The identification of blue diffusion-treated sapphires . In: Gems & Gemology . tape 25 , no. 2 , 1990, p. 115-133 ( gia.edu [PDF; 936 kB ; accessed on June 6, 2020]).
93. ↑ Youtube - Video safe production
94. ↑ wester-mineralien.de - areas of application for high-grade corundum
95. ↑ Entry on aluminum oxide / corundum. In: Römpp Online . Georg Thieme Verlag, accessed on May 21, 2016.

This article was added to the list of excellent articles on November 24, 2018 in this version .