Andradite

from Wikipedia, the free encyclopedia
Andradite
Andradite (lime iron garnet) - Vaskö, Banat, Romania.jpg
Andradite crystal group on calcite from Vaskö, Banat , Romania (exhibited in the Mineralogical Museum of the University of Bonn )
General and classification
other names
  • Allochroit
  • Calcium iron garnet
  • Lime iron garnet
chemical formula Ca 3 Fe 3+ 2 [SiO 4 ] 3
Mineral class
(and possibly department) 		Silicates and Germanates
System no. to Strunz
and to Dana 		9.AD.25 ( 8th edition : VIII / A.08)
51.04.03b.01
Crystallographic Data
Crystal system cubic
Crystal class ; symbol cubic hexakisoctahedral; 4 / m  3  2 / m
Space group Ia 3 d (No. 230)Template: room group / 230
Lattice parameters a  = 12.06 (natural); 12.058 (terminal)  Å
Formula units Z  = 8
Physical Properties
Mohs hardness 6.5 to 7
Density (g / cm 3 ) 3.8 to 3.9 (measured); 3.859 (calculated); 3.8507 (end link)
Cleavage no
Break ; Tenacity uneven to shell-like; brittle
colour yellow, green-yellow to emerald green, dark green, brown to red-brown, rarely colorless or black
Line color White
transparency transparent to translucent
shine Diamond to resin gloss
Crystal optics
Refractive index n  = 1.889

Andradite , also known as calcium iron garnet or lime iron garnet , is a frequently occurring mineral from the group of garnets within the mineral class of " silicates and germanates ". It crystallizes in the cubic crystal system with the idealized composition Ca 3 Fe 3+ 2 [SiO 4 ] 3 , so from a chemical point of view it is a calcium - iron- silicate, which structurally belongs to the island silicates .

Andradite is the iron analogue of grossular (Ca 3 Al 2 [SiO 4 ] 3 ) and uwarowite (Ca 3 Cr 2 [SiO 4 ] 3 ) and forms a mixed crystal series with these , the so-called "ugandite series". Since andradite also forms mixed crystals with the other garnet minerals schorlomite (Ca 3 Ti 4+ 2 [Fe 3+ 2 SiO 12 ]) and kimzeyite (Ca 3 Zr 2 [Al 2 SiO 12 ]), it shows a correspondingly wide spectrum of Composition with more or less large proportions of titanium and zirconium depending on the formation conditions . Since it can also contain other foreign admixtures , it usually comes in different colors, although green-yellow to emerald-green and brown to red-brown colors predominate. Colorless and black andradites are also rarely found.

The mineral is transparent to translucent and typically develops rhombic dodecahedron or trapezoidal shape as well as combinations of these crystal forms, which can be up to five centimeters in size and have a resin-like to diamond-like sheen . In addition, it also occurs in granular to massive mineral aggregates .

Etymology and history

The mineral was first described around 1800 by the Brazilian mineralogist and statesman José Bonifácio de Andrada e Silva , who discovered it on his journey through Norway in the “Wirum” mine near Drammen . Under the name Allochroit Silva described in his notes some of the properties of the mineral such as its yellowish gray to dark straw color (variety Topazolith ) and relatively high hardness ( " just scratched by quartz " translated from quartz barely be scratched ), but was no chemical composition.

The mineral was given its name, which is still valid today, in 1868 from James Dwight Dana , who in his work "A System of Mineralogy" summarized all the lime-iron garnets known up to that time under the name Andradite and thus honored the first discoverer of this mineral type, Andrada e Silva.

classification

The structural classification of the International Mineralogical Association (IMA) is one of the Andradite to Garnet supergroup, where he along with almandine , Calderit , Eringait , Goldmanit , Grossular , Knorringit , Morimotoit , majorite , Menzerit- (Y) , Momoiit , pyrope , Rubinit , Spessartine and Uvarowite form the garnet group with 12 positive charges on the tetrahedrally coordinated lattice position.

Already in the now outdated, but partly still in use 8th edition of the mineral systematics according to Strunz , andradite belonged to the mineral class of "silicates and germanates" and there to the department of " island silicates (nesosilicates)", where together with Goldmanit, Grossular and Uwarowit the independent "Granatgruppe-Ugrandit series" with the system no. VIII / A.08 .

The 9th edition of Strunz's mineral systematics , which has been in force since 2001 and is used by the International Mineralogical Association (IMA), also classifies andradite in the “island silicates” department. This is further subdivided according to the possible presence of additional anions and the coordination of the cations involved , so that the mineral is classified according to its composition and structure in the subdivision of “island silicates without additional anions; Is cations published in octahedral [6] and to find usually greater coordination, "where it along with almandine, Calderit, Goldmanit, Grossular, Henritermierit , Holtstamit , katoite , Kimzeyit , Knorringit, majorite, Morimotoit, pyrope, Schorlomit , Spessartin and Uwarowit the "garnet group" with the system no. 9.AD.25 forms. The garnet compounds blythite, hibschite, hydroandradite and skiagite, which are no longer regarded as minerals, were also included in this group. Wadalite , at that time still grouped with the grenades, proved to be structurally different and is now assigned to a separate group with chloromayenite and fluoromayenite . The garnets irinarassite , hutcheonite , kerimasite , toturite , menzerite (Y) and eringaite described after 2001 would have been classified in the garnet group.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns andradite to the class of "silicates and Germanates" and there in the department of "island silicate minerals ". Here it is together with Goldmanit, Grossular, Uwarovit and Yamatoit (discredited because it is identical to Momoiit) in the "Garnet Group (Ugrandit series)" with the system no. 51.04.03b to be found in the subsection “ Island silicates: SiO4 groups only with cations in [6] and> [6] coordination ”.

Chemism

Andradite with the idealized composition [X] Ca 2+ 3 [Y] Fe 3+ [Z] Si 3 O 12 is the iron analog of grossular ( [X] Ca 2+ 3 [Y] Al [Z] Si 3 O) 12 ) and forms mixed crystals in most other silicate grenades.

On the octahedral Y position, Fe 3+ can be replaced by various cations, depending on the exchange reactions

  • [Y] Fe 3+ = [Y] Al 3+ , (grossular),
  • [Y] Fe 3+ = [Y] Cr 3+ , (uwarowite),
  • [Y] Fe 3+ = [Y] V 3+ , (goldmanite),
  • [Y] Fe 3+ = [Y] Sc 3+ , (Eringaite)

On the dodecahedrally coordinated X position, Ca 2+ can be replaced by Mn 2+ and Fe 2+ , according to the exchange reactions

  • [X] Ca 2+ = [X] Mn 2+ (calderite),
  • [X] Ca 2+ = [X] Fe 2+ (Skiagit)

As with the grossular silicon can also be replaced with four protons (H + ) and a blank (□) in the andradite , according to the substitution

  • [Z] Si 4+ + 4 O 2- = [Z] □ 4+ + 4 OH - (hydroandradite).

The so far OH-richest natural andradite was found in the Wessels Mine in the Kalahari Manganese Field (South Africa) and contains around 35 mol% of the Fe 3+ analog of katoite ( [X] Ca 2+ 3 [Y] Fe 3+ [ Z] □ 3 (OH) 12 ).

In melanite, titanium-containing andradite, titanium is incorporated in the octahedral Y position mainly via two exchange reactions:

  • [Y] Fe 3+ + [Z] Si 4+ = [Y] Ti 4+ + [Z] Fe 3+ (Schorlomite)
  • 2 [Y] Fe 3+ = [Y] Ti 4+ + [Y] Fe 2+ (morimotoite)

Crystal structure

Andradite crystallizes with cubic symmetry in space group Ia 3 d (space group no. 230) with 8 formula units per unit cell . There are numerous provisions for the edge length of the cubic unit cell of both natural mixed crystals and synthetic andradites. Among other things, the lattice parameter for the pure Andradite  terminal is given as a  = 12.048 Å or a = 12.058 Å. Template: room group / 230

The structure is that of garnet . Calcium (Ca 2+ ) occupies the dodecahedral X positions surrounded by 8 oxygen ions, iron (Fe 3+ ) the octahedral Y position surrounded by 6 oxygen ions and the tetrahedral Z position surrounded by 4 oxygen ions is exclusively silicon (Si 4+ ) occupied.

Natural andradites often show sector zoning and are optically slightly birefringent , which is usually interpreted as an indication of a lower, non-cubic symmetry. For a birefringent andradite from a skarn from the Sonoma area in Nevada, USA, for example, triclinic symmetry was determined, caused by an orderly distribution of Fe 3+ and Al on the 8 different octahedrally coordinated positions of the triclinic garnet structure.

In recent investigations with high-resolution synchrotron - X-ray diffraction , however, could be shown that birefringent Andradite a mixture 2 - 3 shells of different composition are. All garnets of these adhesions are cubic with slightly different lattice constants . It is these different grenade lattice constants that lead to lattice stresses and consequently stress birefringence .

properties

Heated up before the soldering tube , andradite forms a black, magnetic ball.

Modifications and varieties

  • Demantoid is an andradite colored yellow-green to dark green by foreign admixtures of chrome . It was named around 1870 by Nils von Nordenskiöld , who discovered the "greenish pebbles" in the Urals, which were later recognized as andradites.
  • Hydroandradite (Ca 3 Fe 3+ 2.0 (SiO 4 ) 2.71-2.81 (H 4 O 4 ) 0.29-0.19 ) does not count as an independent mineral, but as a variety of andradite.
  • Melanite (after Abraham Gottlob Werner , 1799) is regarded as a titanium-rich variety of andradite and named after the Greek word μέλας for black , as it occurs predominantly in gray-black to pitch-black crystals or coarse aggregates.
  • Topazolite (=  similar to topaz ) is a light yellow to cognac-colored andradite variety.

  • Light green demantoids from Antetezambato (Tetezambato), Ambanja district , Madagascar ( overall size : 9.0 cm × 6.0 cm × 3.8 cm)

  • Yellowish brown topazolites from the same site ( overall size : size: 7.7 cm × 6.5 cm × 2.6 cm)

  • Black melanite from the Kayes region , Mali (size: 5.5 cm × 5.5 cm × 4.5 cm)

Education and Locations

Similar to Grossular also Andradit forms by contact metasomatism (certain rock material displacement components) upon supply of iron in skarns and in kontaktmetamorph converted iron ore - deposits . He also found as Nebengemengteil in nepheline - syenites , phonolites and other alkaline rocks. Occasionally, andradite also occurs in alpine fissures when green slate ( chlorite slate ) or similar iron-rich rocks are present as adjacent rock. Accompanying minerals include calcite , chlorite , dolomite , epidote , magnetite , spinel and vesuvianite .

As a frequent mineral formation, andradite can be found at many localities, whereby so far (as of 2013) around 1400 localities are known. In addition to its type locality Drammen, the mineral occurred in Norway, among other places, in several places in the province of Buskerud (Kongsberg, Lier, Nedre Eiker) and in some places in the provinces of Aust-Agder (Arendal, Gjerstad), Nordland , Oppland (Grua, Nordmarka ), Telemark (Porsgrunn, Skien) and Vestfold (Larvik, Sandefjord).

The “Kohse” pit near Tenkawa in the district of Yoshino-gun ( Nara prefecture ) on the Japanese island of Honshū, where several centimeters large and partly iridescent crystal steps came to light, is known for its extraordinary andradite finds. These so-called "Rainbow Grenade" (English rainbow garnet ) are, however, also found in Mexico. Crystals up to four centimeters in size are known from the Sinerechenskoye deposit ( Kawalerowo administrative district ) in the Primorye region of Russia, and demantoid crystals up to three centimeters in size have been found in Val Malenco in the Italian province of Sondrio .

In Germany, andradite has so far been found in many places: in the Black Forest in Baden-Württemberg; in the Fichtelgebirge , Franconian Forest and Bavarian Forest in Bavaria; near Rachelshausen , Hirzenhain and Hochstädten (Bensheim) in Hesse; near Bad Harzburg and Sankt Andreasberg in Lower Saxony; in many places in the Eifel (Rhineland-Palatinate), in the Saxon Ore Mountains and Vogtland as well as at Unterbreizbach and Sparnberg in Thuringia.

In Austria the mineral was found near Badersdorf and Pauliberg in Burgenland, near Andreaskreuz in the municipality of Hüttenberg and near Wollanig near Villach in Carinthia, in several places in the Lower Austrian Waldviertel and the Salzburg Hohen Tauern as well as in some places in Styria, Tyrol and Vorarlberg.

In Switzerland, andradite has so far mainly appeared in the cantons of Graubünden and Valais , but could also be found near Oberbargen in Schaffhausen.

Other locations include Afghanistan, Antarctica, Argentina, Ethiopia, Australia, Azerbaijan, Bolivia, Brazil, Bulgaria, Chile, China, the Democratic Republic of the Congo, Ecuador, Finland, France, Greece, Greenland, Guinea, Honduras, Iceland, India, Iran, Israel, Jeman, Canada, Kazakhstan, Kenya, Kyrgyzstan, Madagascar, Malawi, Mali, Morocco, Mexico, Mongolia, Myanmar, Namibia, New Zealand, Norway, Pakistan, Palestine, Papua New Guinea, Paraguay, Peru, on the Philippines, Poland, Portugal, Romania, the Solomon Islands, Sweden, Serbia, Slovakia, Spain, Sri Lanka, South Africa, South Korea, Taiwan, Tajikistan, Tanzania, Thailand, the Czech Republic, Turkey, Ukraine, Hungary, Uzbekistan, the United Kingdom (Great Britain), the United States of America (USA) and Cyprus.

  • Hematite , overgrown by red andradite from the "Wessels Mine", Hotazel, Kalahari Manganfeld, North Cape, South Africa (size: 4.2 cm × 2.8 cm × 2.4 cm)

  • Yellow andradite and rhodochrosite , also from the "Wessels Mine" (size: 5.2 cm × 4.7 cm × 3 cm)

  • Iridescent "rainbow" andradite from the "Kohse" pit, Honshū, Japan (size: 10 cm × 9 cm × 8 mm)

  • Topazolite from Wurlitz in the Fichtel Mountains . Exhibited in the Mineralogical Museum Bonn

Use as a gem stone

Pendant with faceted demantoids

Like most garnets, andradite or its varieties demantoid and topazolite are used as a valuable gemstone if they are of appropriate quality . Due to the variety of colors, due to the extensive mixed crystal formation of the garnet, the gemstone trade has meanwhile switched to assigning the garnets to the individual types of garnet, not according to their chemical composition, which is often difficult to determine, but according to their respective color nuances, which accordingly only serve as color names. For example, the green garnets are called either demantoid, hydrogrossular or tsavorite or tsavolite, although the latter is actually chemically one of the grossulars .

Depending on the color, it can be confused with ruby and spinel (red), peridot and emerald (green), topaz and hyacinth (yellowish to brownish) and the multi-colored tourmaline .

See also

literature

  • Maximilian Glas and others: garnet. The minerals of the garnet group: precious stones, jewelry and lasers (= Christian Weise [Hrsg.]: ExtraLapis . Volume 9 ). Christian Weise Verlag, 1995, ISBN 3-921656-35-4 , ISSN  0945-8492 .

Web links

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

Individual evidence

  1. ↑ a b c d e f g h Hugo Strunz , Ernest H. Nickel : Strunz Mineralogical Tables. Chemical-structural Mineral Classification System . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p.  540-542 .
  2. ^ David Barthelmy: Andradite Mineral Data. In: webmineral.com. Retrieved January 20, 2019 .
  3. ↑ a b c d DK Teertstra: Index-of-refraction and unit-cell constraints on cation valence and pattern of order in garnet-group minerals . In: The Canadian Mineralogist . tape 44 , 2006, pp. 341–346 (English, rruff.info [PDF; 192 kB ; accessed on January 20, 2019]).
  4. ↑ a b Andradite . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America . 2001 (English, handbookofmineralogy.org [PDF; 73  kB ; accessed on January 20, 2019]).
  5. ↑ JB d'Andrada: Brief statement of the properties and characteristics of some new fossils from Sweden and Norway, along with some chemical remarks about them . In: General Journal of Chemistry . tape 4 , 1800, p. 28–39 ( rruff.info [PDF; 2.5 MB ; accessed on January 20, 2019]).
  6. ^ JD Dana, GJ Brush: A System of Mineralogy . 5th edition. John Wiley and Sons, New York 1868, p. 268-270 , E. Lime-Irongarnet; Andradite (English, rruff.info [PDF; 862 kB ; accessed on January 20, 2019]).
  7. ^ A b c Edward S. Grew, Andrew J. Locock, Stuart J. Mills, Irina O. Galuskina, Evgeny V. Galuskin and Ulf Hålenius: IMA Report - Nomenclature of the garnet supergroup . In: American Mineralogist . tape 98 , 2013, p. 785–811 ( main.jp [PDF; 2,3 MB ; accessed on January 20, 2019]).
  8. ↑ HG Huckenholz, HS Yoder: Andradite stability relations in the CaSiO 3 -Fe 2 O 3 join up to 30 Kb. In: New Yearbook for Mineralogy, Abhandlungen . tape 114 , 1971, p. 246–280 (English, htracyhall.org [PDF; 2.2 MB ; accessed on January 20, 2019]).
  9. ^ HG Huckenholz, D. Knittel: Uvarovite: Stability of uvarovite-andradite solid solutions at low pressure . In: Contributions to Mineralogy and Petrology . tape 56 , 1976, pp. 61-76 , doi : 10.1007 / BF00375421 (English).
  10. ↑ Biswajit Ghosh and Tomoaki Morishita: Andradite-Uvarovite solid solution from hydrothermally altered podiform chromitite, Rutland ophiolite, Andaman, India . In: The Canadian Mineralogist . tape 49 , 2011, p. 573-580 , doi : 10.3749 / canmin.49.2.573 (English).
  11. ↑ Simona Quartieri, Roberta Oberti, Massimo Boiocchi, Maria Chiara Dalconi, Federico Boscherini, Olga Safonova, Alan B. Woodland: Site preference and local geometry of Sc in garnets: Part II. The crystal-chemistry of octahedral Sc in the andradite-Ca 3 Sc 2 Si 3 O 12 join . In: American Mineralogist . tape 91 , 2006, p. 1240–1248 (English, rruff.info [PDF; 432 kB ; accessed on January 20, 2019]).
  12. ↑ Georg Amthauer, Kerstin Katz-Lehnert, Dominique Lattard, Martin Okrusch and Eduard Woermann: Crystal chemistry of natural Mn 3+ -bearing calderite-andradite garnets from Otjosondu, SW A / Namibia . In: Journal of Crystallography . tape 189 , 1989, pp. 43–56 (English, researchgate.net [PDF; 693 kB ; accessed on April 28, 2018]).
  13. ↑ Alan B. Woodland, Charles R. Ross: A crystallographic and Mössbauer spectroscopy study of Fe 3 2+ Al 2 Si 3 O 12 -Fe 3 2+ Fe 2 3+ Si 3 O 12 , (almandine- “skiagite”) and Ca 3 Fe 2 3+ Si 3 O 12 -Fe 3 2+ Fe 2 3+ Si 3 O 12 (andradite- “skiagite”) garnet solid solutions . In: Physics and Chemistry of Minerals . tape 21 , 1994, p. 117-132 , doi : 10.1007 / BF00203142 (English).
  14. ^ A b Georg Amthauer, George Rossman: The hydrous component in andradite garnet . In: The American Mineralogist . tape 83 , 1998, pp. 835–840 (English, minsocam.org [PDF; 78 kB ; accessed on May 7, 2018]).
  15. ↑ Thomas Armbruster: Structure refinement of hydrous andradite, Ca 3 Fe 1.54 Mn 0.20 Al 0.26 (SiO 4 ) 1.65 (O 4 H 4 ) 1.35 , from the Wessels mine, Kalahari manganese field, South Africa . In: European Journal of Mineralogy . tape 7 , 1995, p. 1221–1226 , doi : 10.1127 / ejm / 7/5/1221 (English).
  16. ^ BJ Skinner: Physical properties of end members of the garnet group . In: American Mineralogist . tape 41 , 1956, pp. 428–436 (English, minsocam.org [PDF; 509 kB ; accessed on January 20, 2019]).
  17. ^ GA Novak and GV Gibbs: The crystal chemistry of the silicate garnets . In: The American Mineralogist . tape 56 , 1971, p. 791–825 (English, rruff.info [PDF; 2,3 MB ; accessed on May 4, 2018]).
  18. ↑ Kathleen J. Kingma, James W. Downs: Crystal-structure analysis of a birefringent andradite . In: American Mineralogist . tape 74 , 1989, pp. 1307–1316 (English, rruff.info [PDF; 735 kB ; accessed on January 20, 2019]).
  19. ↑ sytle M. Antao: Three cubic phases intergrown in a birefringent Andradite-grossular garnet and Their implications . In: Physics and Chemistry of Minerals . tape 40 , 2013, p. 705-716 , doi : 10.1007 / s00269-013-0606-4 (English).
  20. ↑ sytle M. Antao: The mystery of birefringent garnet: is the symmetry lower than cubic? In: Powder Diffraction . tape 28 , 2013, p. 281–288 (English, cambridge.org [PDF; 375 kB ; accessed on June 16, 2018]).
  21. ^ Friedrich Klockmann : Klockmanns textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp.  666–669 (first edition: 1891).
  22. ↑ Thomas Fehr, Maximilian Glas, Joachim Zang: The extraLapis garnet dictionary . In: garnet. The minerals of the garnet group: precious stones, jewelry and lasers (= Christian Weise [Hrsg.]: ExtraLapis . Volume 9 ). Christian Weise Verlag, 1995, ISBN 3-921656-35-4 , ISSN  0945-8492 , p. 4 .
  23. ↑ Hans Lüschen: The names of the stones. The mineral kingdom in the mirror of language . 2nd Edition. Ott Verlag, Thun 1979, ISBN 3-7225-6265-1 , p. 272 .
  24. ^ Helmut Schrätze , Karl-Ludwig Weiner : Mineralogie. A textbook on a systematic basis . de Gruyter, Berlin; New York 1981, ISBN 3-11-006823-0 , pp.  679 .
  25. ^ Andradite. In: mindat.org. Hudson Institute of Mineralogy, accessed January 20, 2019 .
  26. ^ Andradite picture gallery from the Kohse Mine, Tenkawa, Yoshino-gun, Nara, Kinki Region, Honshū, Japan. In: mindat.org. Hudson Institute of Mineralogy, accessed January 20, 2019 .
  27. ↑ Petr Korbel, Milan Novák: Mineral Encyclopedia (=  Dörfler Natur ). Edition Dörfler im Nebel-Verlag, Eggolsheim 2002, ISBN 978-3-89555-076-8 , p. 198 .
  28. ↑ Locations for andradite at the Mineralienatlas and at Mindat
  29. ↑ Bernhard brother embellished stones. Recognizing imitations and manipulations in gemstones and minerals . Neue Erde, Saarbrücken 2005, ISBN 3-89060-079-4 , p. 68-69 .
  30. ^ 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. 122 .