diamond


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diamond
Алмазы в Центре сортировки алмазов в городе Мирный, Якутия.jpg
Rough diamonds with typical octahedron shape from the diamond sorting center in Mirny , Republic of Sakha (Yakutia)
General and classification
chemical formula C.
Mineral class
(and possibly department)
elements
System no. to Strunz
and to Dana
1.CB.10 ( 8th edition : I / B.02)
03/01/06/01
Similar minerals structurally related to sphalerite (zinc blende)
Crystallographic Data
Crystal system cubic
Crystal class ; symbol cubic hexakisoctahedral; 4 / m  3  2 / m
Space group Fd 3 m (No. 227)Template: room group / 227
Frequent crystal faces {111}
Twinning Penetration twins according to the spinel law
Physical Properties
Mohs hardness 10
Density (g / cm 3 ) 3.52
Cleavage {111} perfect
Break ; Tenacity shell-like to splintery
colour colorless, different colors possible due to contamination or lattice defects
Line color White
transparency transparent to sub-transparent / translucent
shine Diamond luster
Crystal optics
Refractive index n  = 2.4076 (red, 687 nm) to 2.4354 (blue, 486 nm)
Birefringence none, as it is optically isotropic
Axis angle not applicable as it is optically isotropic
Pleochroism unknown
Other properties
Chemical behavior almost inert , at high temperatures reactions with hydrogen, oxygen and fluorine; Easily soluble in metal melts of carbon-soluble metals (e.g. iron, nickel, cobalt, chromium, platinum metals), sometimes with formation of carbide
Special features highest melting point of a mineral, thermal conductivity 1000–2500 W / (m · K) (five times better than silver ), electrical conductivity : insulator , sometimes fluorescent , compression modulus = 442 GPa

Diamond is the cubic modification of carbon and, as a naturally occurring solid, is a mineral from the mineral class of the elements . Diamond usually forms octahedral crystals , often with curved and streaky surfaces. Other shapes observed are the tetrahedron , dodecahedron and the cube . The crystals are transparent, colorless or colored by impurities (e.g. nitrogen or boron ) or crystal lattice defects green, yellow, brown and, more rarely, orange, blue, pink, red or gray to black.

Diamond is the hardest natural substance. In the Mohs hardness scale it has a hardness of 10. Its grinding hardness according to Rosiwal (also absolute hardness ) is 140 times greater than that of corundum . However, the hardness of the diamond is different in different crystal directions ( anisotropy ). This makes it possible to diamond with diamond grinding . In the diamond powder used for this, the crystals are in every orientation (statistical isotropy), so that the hardest of them always have an effect on the body to be ground.

Diamond is optically isotropic with high light refraction and high dispersion . It shows fluorescence and phosphorescence and is triboelectric . It has the highest thermal conductivity of all known minerals.

The weight of individual diamonds is traditionally given in carats , a unit that corresponds exactly to 0.2 grams (see section “ Weight in carats ”). An untreated, i.e. H. in particular, uncut diamond is called a rough diamond .

Etymology and history

Exhibition in Amsterdam, 1955

The name diamond is derived from the Late Latin diamantem , accusative of diamas off a gräzisierenden modification of Adamas , akk. adamanta , from Greek ἀδάμας , adámas , "invincible". In classical Latin, as in Greek, especially hard materials were referred to as adamas , such as steel by Hesiod, diamond by Plato and Theophrastus and sapphire by Pliny .

The oldest diamond finds are reported from India , allegedly as early as the 4th millennium BC. Even then, diamonds were said to have magical effects, which is why they were also used as talismans . Diamonds were also known and valued by the ancient Romans .

The use of diamonds as a tool was already described by Pliny the Elder in his work Naturalis historia , XXXVII 60. Around 600 AD the first diamond was reported on the Indonesian island of Borneo , but although India was no longer the only source, they remained Indonesian finds insignificant, as the number was too small and the transport to the trading cities too far. It was only in the 13th century that it was discovered that diamonds can be worked, but this was rejected in India because the stones could allegedly lose their magical powers. Today's typical brilliant cut was only developed around 1910.

In the 18th century the Indian and Indonesian mines gradually ran out. When a Portuguese was looking for gold in Brazil , he discovered the first diamond outside of Asia. This find caused a "diamond rush". The first diamond in the mother rock kimberlite was found in 1869 in Kimberley in South Africa . A year later, South Africa took over the role of the main supplier, as finds in Brazil also became rarer.

At the World Exhibition in Philadelphia in 1876 , a diamond-studded stone circular saw was shown to the general public for the first time. In 1908 diamonds were discovered on the diamond coast of German South West Africa , and in 1955 the first diamond was finally artificially produced. The first diamond on the ocean floor was not found until 1961. Today Russia is the main supplier of diamonds.

Further first finds
year Country
1826 Russia
1851 Australia (first in Australia )
1867 South Africa (first in Africa )
1901 Venezuela
1906 USA (state of Arkansas )
1906 on the territory of today's Democratic Republic of the Congo (then Belgian Congo )
1908 Namibia (then German South West Africa )
1912 Angola (then Portuguese )
1920 West coast of Africa ( Ghana , then British colony Gold Coast )
1969 China
1992 Canada

classification

In the meanwhile outdated, but still in use 8th edition of the mineral classification according to Strunz , the diamond belonged to the mineral class of the "elements" and there to the department of "semimetals and non-metals", where together with chaoite , fullerite , graphite , lonsdaleite and moissanite it was an independent one Group formed.

The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and is used by the International Mineralogical Association (IMA), also assigns the diamond to the “elements” class and there to the “semimetals (metalloids) and non-metals” division. However, this section is further subdivided according to the related chemical elements, so that the mineral can be found in the sub-section “Carbon-Silicon Family”, where it only forms the unnamed group 1.CB.10 together with Lonsdaleit .

The systematics of minerals according to Dana also assigns the diamond to the class and department of the same name of "elements". Here it is together with graphite, lonsdaleit, chaoite and fullerite in the "carbon polymorph" with the system no. 01.03.06 can be found in the sub-section " Elements: Semi-Metals and Non-Metals ".

Crystal structure

Cubic crystal structure of diamond. The grid consists of two mutually penetrating face-centered cubic (fcc) grids. Each carbon atom is covalently bonded to four neighboring atoms.

Diamond consists exclusively of pure, cubic crystallized carbon. Even if the internal structure theoretically consists of pure carbon, the free atomic bonds at the interfaces of the crystal are still saturated with oxygen or hydrogen.

In diamonds the carbon atoms are tetrahedrally bound; that is, each atom has four symmetrically aligned bonds to its closest neighbors. The high hardness is due to the very high binding energy of the complete in sp 3 - hybridization present chemical bonds.

properties

Diamond oxidizes in pure oxygen at approx. 720 ° C, in air also from 720 ° C at a slower reaction rate to (gaseous) carbon dioxide . If a diamond with a diameter of a few millimeters that has been heated to a yellow glow is placed in liquid, i.e. cryogenic, oxygen , it sinks and burns with glowing appearance to carbon dioxide, which is solid. The enthalpy of reaction of 395.7 kJ / mol is 1.89 kJ / mol greater than that of graphite. To burn diamond in a gas flame, you need an excess of oxygen. Diamond powder with a suitable grain size around 50 micrometers burns in a shower of sparks after contact with a flame, similar to coal powder. Accordingly, pyrotechnic sets can also be manufactured on the basis of diamond powder. While the spark color is comparable to coal powder, a very linear trajectory is observed due to the approx. Twice higher density. It reacts with hydrogen at high temperatures to form hydrocarbons.

Diamond dissolves in melts of carbon-dissolving metals such as iron, nickel, cobalt, chromium, titanium, platinum, palladium and their alloys. The larger the grain or the crystal, the lower the rate of conversion - in all cases - according to the ratio of reactive surface to volume.

Age determination

The age of the diamonds can be determined from their inclusions. These inclusions arise at the same time as the diamond that surrounds them and are often composed of surrounding silicate minerals . The age of the silicate minerals can be determined with geochronology based on their isotopic composition; mainly the decay systematics of 147 Sm to 143 Nd and 187 Re to 187 Os are used. Based on the now large database of isotope data, it can be determined that diamond formation took place again and again at different times across all geological ages, and that there are not only very old diamonds that are more than three billion years old, but also younger ones that are still reach an age of several hundred million years. The oldest known diamond has been dated to an age of 4.25 billion years.

Modifications and varieties

In addition to cubic crystallizing diamond, the following carbon modifications are known:

Diamond is metastable at room temperature and normal pressure . However, the activation energy for the phase transition to the stable modification (graphite) is so high that conversion to graphite practically does not take place at room temperature.

Ballas (radial, fibrous) and carbonado (black, porous polycrystalline diamond, which so far has only been found in Central Africa and South America) are special diamond varieties whose crystal structures have increased lattice defects due to unfavorable growth conditions .

Education and Locations

Video about the creation of diamonds
Octahedral diamond of about 1.8 carats (6 mm) in kimberlite from the "Finsch Diamond Mine", South Africa

Diamonds that are large enough for jewelry production are only formed in the earth's mantle under high pressures and temperatures, typically at depths between 250 and 800 kilometers and at temperatures of 1200 to 1400 ° C. In terms of depth, the primary places of origin of the diamonds are on the one hand the (1) lower asthenosphere and the mantle transition zone in the upper mantle and on the other hand (2) the border region of the upper / lower mantle and the uppermost lower mantle. Inclusions from the diamond of type (1) exhibit eklogitisches toward parent rock in the mantle, while the parent rock of the type (2) is likely meta- peridotitisches is material. It is assumed that diamonds crystallize in a melt in nature, which would not only agree with the occurrence of partial rock melts in the two above-mentioned areas of the earth's mantle, but would probably also be dependent on it. Not only do the two types of host rock in the earth's mantle indicate a connection with subducted ocean floor, this circumstance would also explain the presence of rock melts due to dewatering reactions during mineral phase transitions. Gas-rich volcanic rocks, so-called kimberlites and in individual cases also lamproites (Argyle mines in Kimberley (Australia) ), transport fragments of the earth's mantle with the diamonds it contains to the earth's surface when they erupt , where they are in the diatrems ( pipes ), the volcanic eruptive vents , being found. Corresponding conditions, i.e. the presence of carbon and corresponding pressure and temperature, are usually only given in the upper mantle from the Archean and Hadaic times, which is why exploration is mostly limited to the correspondingly old crustal sections.

The respective transport time from the depths is estimated at a few hours, so that, due to the speed, there is no phase change to graphite. The last phase of the eruption occurs at supersonic speeds. Diamonds are foreign or xenocrystals in kimberlite and lamproit and are not chemically stable in these magmas (metastable). So you can always observe signs of dissolution in natural diamonds. From their occurrence in diatrems, the diamond crystals can be transported away by natural weathering processes, during which they remain intact due to their hardness, and enriched in sedimentary rocks , which are one of the main sources of this mineral today. Such occurrences are called alluvial . In particular, the best, low-inclusion diamonds survive the transport undamaged, so that alluvial deposits contain a particularly large number of diamonds of gem quality.

Metamorphic so-called UHP microdiamonds ( Ultra High Pressure ) have been found in the Ore Mountains , in Greece and in Kazakhstan , for example . The deposits are tied to sections of the earth's crust that were exposed to high pressures and temperatures during mountain formation and metamorphosis .

Origin of the carbon

Carbon occurs relatively rarely in the earth's mantle, either it represents a residue of the carbon that did not go into the crust during the differentiation of the earth's body, or it was brought back to these depths by the thrust or subduction of oceanic crust. Therefore diamonds sometimes have isotopic compositions that indicate a biogenic origin of the carbon and salty inclusions.

Earthly occurrences

Map showing regions where diamonds were extracted
The Siberian Udachnaya open-cast mine in the largest diamond deposit in Russia.

The largest diamond deposits are in Russia , Africa , especially in South Africa , Namibia , Angola , Botswana , the Democratic Republic of the Congo and Sierra Leone , in Australia , Canada and Brazil . Meanwhile diamonds have been found on every continent .

A total of around 700 locations for diamond are known so far (as of 2015). In Germany, diamonds were found on the Nördlinger Ries and near the Saidenbach dam near Forchheim.

Since diamonds are only stable on earth from a depth of approx. 140 km, the largest specimens can be found when they came up particularly quickly (usually with magmas) from at least this depth; diamonds from the lower mantle have even been detected become. Diamonds that have come to the surface of the earth through purely tectonic processes ( exhumation ) are usually relatively small (diameter usually less than 1 mm).

Dismantling

Diamonds are mostly extracted from pipes of extinct volcanoes, which are usually mined vertically downwards in their chimney filling , first in opencast mines, then underground. The host rock is ground up in order to separate the diamond crystals from the rock composite. Extensive opencast mines of this type are operated in Botswana, Russia and Angola. In Namibia and South Africa, diamonds are also found in the inland in the gravel terraces of some river valleys and in the partly desert-like coastal strips on the Atlantic in alluvial soils as well as submarine on the continental shelf , where they reached after erosion of their primary deposit by external natural influences, with other river scree components. The mining in these deposits is very space-intensive and is carried out by mechanical selection from the extracted loose sediments. It has a major impact on the affected ecosystems. Specially constructed ships are used for mining underwater, on which the diamonds are washed out of the sucked in sand.

Economically minable diamond deposits mostly occur in kimberlite rocks that have penetrated rock complexes that are at least 2.5 billion years old. These rock complexes are part of the geologically oldest areas of today's continents, the so-called mainland cores or cratons , which are characterized by an extremely thick lithosphere (300 km). The formation of the diamond-containing kimberlites and thus also the essential diamond deposits is linked to so-called plumes ; In these areas, material rises from the earth's mantle, heats the overlying lithosphere strongly and leads to volcanism (see also hotspot ).

The world production of natural diamonds (for example by the Rio Tinto Group ) is around twenty tons per year, which currently only covers around 20% of industrial demand. This is why synthetically produced diamonds, whose properties such as toughness, crystal habit, conductivity and purity can be precisely influenced, are increasingly filling this gap in demand.

Extraterrestrial formation and occurrence

Microdiamonds are mainly formed when meteorite impacts occur : the high temperatures and pressure conditions that occur during this process compress earthly carbon so much that small diamond crystals and also Lonsdaleite form, which are deposited from the explosion cloud and are still today in the vicinity of meteorite craters such as the Barringer Crater can be proven. Microdiamonds also occur in finds of iron meteorites and ureilitic achondrites , where they were probably formed from graphite by shock events. Tiny diamonds, often called nanodiamonds because of their typical size of just a few nanometers, also occur in the form of presolar minerals in primitive meteorites.

Carbonaceous chondrites

Carboniferous chondrite

Carbonaceous chondrites are stone meteorites with a comparatively high (up to 3%) proportion of carbon. These sometimes contain tiny, nanometer-sized diamonds that were formed outside of our solar system .

Synthetic manufacture

Synthetic diamonds
Synthetic diamond single crystal with a diameter of 92 mm and a weight of 155 carats

The production of synthetic diamonds was first achieved on February 15, 1953 by the physicist Erik Lundblad at the Swedish electrical engineering group ASEA .

In diamond burial , carbon is pressed from the ashes of the deceased into diamonds.

production method

High pressure high temperature process

Since 1955 it has been possible to manufacture artificial diamonds with the help of the so-called high-pressure high-temperature process (HPHT - English: high-pressure high-temperature ). In this process, graphite is pressed together in a hydraulic press at pressures of up to 6 gigapascals (60,000 bar ) and temperatures of over 1500 ° C. Under these conditions diamond is the thermodynamically more stable form of carbon, so the graphite converts to diamond. This conversion process can be accelerated by adding a catalyst (usually iron carbonyl ). Even with a catalyst, the conversion process still takes a few weeks. Analogous to diamond, cubic boron nitride (CBN) can be produced from the hexagonal modification of boron nitride using high-pressure, high-temperature synthesis. CBN does not quite reach the hardness of diamond up to temperatures of approx. 700 ° C, but is resistant to oxygen at high temperatures, for example.

Detonation Synthesis

Other methods of generating high temperatures and pressures are so-called detonation synthesis and shock wave synthesis. In detonation synthesis, a distinction is made between the detonation of a mixture of graphite and explosive or exclusively the detonation of explosive substances. In the case of the latter, an explosive mixture of TNT (trinitrotoluene) and RDX ( hexogen ) is detonated in a sealed container. The explosives provide the required energy and are at the same time a carbon carrier. In shock wave synthesis, the pressure required to convert carbon material into diamond is brought about by the action of an external shock wave, also triggered by an explosion. The explosion compresses a capsule filled with carbon material. This force causes the carbon material inside to be converted into diamond. Industrial diamond is just as hard as natural diamond.

layers

An alternative to the production of artificial diamond is the coating of substrates by means of chemical vapor deposition (engl. Chemical vapor deposition , CVD). A CVD diamond layer a few micrometers thick is deposited on the substrates , for example hard metal tools, in a vacuum chamber . The starting material is typically a gas mixture of methane and hydrogen , the former serving as a carbon source.

According to Ostwald's rule of levels , mainly metastable diamond should be deposited; According to the Ostwald-Volmer rule , mainly graphite is formed due to its lower density. With atomic hydrogen it is possible to decompose graphite selectively and to promote the formation of diamond. Atomic hydrogen (H) is created in a thermally or electrically heated plasma from molecular hydrogen gas (H 2 ). The substrate temperature must be below 1000 ° C in order to prevent the conversion into the stable graphite. Growth rates of several micrometers per hour can then be achieved.

As a further development, with the help of the technology of plasma coating, for example with PECVD, layers of so-called diamond-like carbon ( DLC : diamond-like carbon ) that are only a few nanometers to micrometers thick can be produced. These layers combine very high hardness and very good sliding friction properties at the same time. Depending on the coating parameters, they contain a mixture of sp 2 - and sp 3 - hybridized carbon atoms. These layers are therefore not diamond. However, these layers have certain properties of the diamond and are therefore referred to as "diamond-like" or "diamond-like". By controlling the process and the choice of precursor material , many types of carbon layers, from hard hydrogen-free to very elastic hydrogen-containing layers, can be produced.

Homo- and heteroepitaxy

Using chemical vapor deposition (MWPCVD) supported by a microwave plasma, it is possible to produce thick diamond bodies on thin diamond substrates or on lattice-adapted foreign substrates ( heteroepitaxy ). The successful production of a disc-shaped diamond with a weight of 155 carats and a diameter of 92 mm in 2016 was based on the latter process. The process consists in that, on the one hand, carbon is released from hydrocarbons (e.g. methane ) in the plasma and is deposited; on the other hand, a high proportion of atomic hydrogen in the plasma ensures that all non-diamond-like deposited structures are removed again. In 2008, the most promising substrate for production of heteroepitaxial diamond wheels is a multilayer structure of an iridium layer on yttrium -stabilized zirconium (IV) oxide (YSZ), which on a single crystal silicon - wafer was deposited.

Further processing

This commercially successful route provides diamond powder in various finenesses. The synthetically produced rough diamonds are first mechanically crushed (grinding in ball mills ). Impurities from residues of the starting materials on the surface of the diamond particles, such as non-flammable impurities or unconverted graphite residues , are removed chemically. In the case of coarser grain sizes, classification is carried out by sieving. Micro-grains, on the other hand, have to be sedimented. For this purpose, the diamond powder is placed in a water basin. The sedimentation speed of a spherical particle can be calculated with the help of Stokes' law . The upper layers of the water-diamond powder mixture are carefully suctioned off and physically dried after each sedimentation period.

Magnetic diamond

At the Rensselaer Polytechnic Institute in Troy it was possible to produce magnetic diamonds. They are only five nanometers in size and have their own magnetic field . The effect is based on a defect in the crystal lattice. Applications of the health-friendly carbon are predicted primarily in medicine.

Monocrystalline diamond powder

Monocrystalline industrial diamond ( single crystal ) is relatively inexpensive and can be produced in large quantities. In industrial technology, it is therefore widely used in grinding , lapping and polishing processes. The diamond has a monocrystalline lattice structure, the sliding planes are oriented parallel to the optical axis (111 plane). When loaded, the monocrystalline diamond grain breaks along the parallel cleavage planes. This results in grains in block form with sharp cutting edges. In symbolic terms, a monocrystalline diamond grain breaks like a salami that is cut into slices ("salami slice model").

Polycrystalline diamond powder

A polycrystalline (industrial) diamond ( polycrystalline ) is composed of a large number of tiny diamond grains. When loaded, small corners and edges break out of the diamond grain, so that new, sharp cutting edges are created again and again (self-sharpening effect). This characteristic enables high removal rates and, at the same time, the finest surfaces to be achieved. It is suitable for lapping and polishing extremely hard materials such as ceramics or sapphire glass.

Nanodiamond

Nanodiamond powder is used in various applications and research areas. The large volume-to-surface ratio creates new physical and chemical properties. Nanodiamonds, for example, have perfect lubricating properties and are therefore added to lubricating oils. Another area of ​​application for nanodiamonds is said to be cancer therapy.

Natural diamond powder

The monocrystalline natural diamond powder is preferably used for the production of electroplated diamond tools. As a waste product of the jewelry industry, it is very rare and correspondingly expensive.

Coated diamond powder

SEM image of nickel-coated diamond powder

Monocrystalline industrial diamond powder coated with nickel , copper or titanium is used, among other things, for the production of electroplated diamond tools.

Use as a gem stone

Natural brilliant cut diamonds

A diamond has a very high refraction and a strong shine , paired with a striking dispersion, which is why it is mainly used as a gemstone to this day . Its brilliance is based on innumerable internal light reflections, which are caused by the careful grinding of the individual facets, which must be in specially selected angular relationships to one another. The aim is to allow a high percentage of the incident light to exit the stone again in the direction of the viewer through reflections inside the stone. In the meantime, cuts and their effects are simulated on computers and the stones are ground on machines in order to achieve optimal results through an exact execution. Only a quarter of all diamonds are qualitatively suitable as gem stones. Only a small fraction of this meets the criteria that are placed on gemstones today: Sufficient size, suitable shape, high purity, freedom from defects, quality of cut, brilliance, color dispersion, hardness, rarity and, depending on the wishes, color or colorlessness.

In the early Middle Ages , the diamond had no special value due to the lack of processing options, and mostly only the colored stones were called precious stones.

Probably beginning in the 14th century and up to the 16th century, diamonds were cut into facets with a smooth cleavage surface upwards and downwards in a curved shape. This cut was called the rose cut , later variants with several facet levels the "Antwerp rose". These diamonds were then set in silver over a foil-covered recess that was polished and sometimes also had impressions of the facets of the rose cut to increase the reflection.

With the invention of better grinding wheels in the 17th century, it was possible to grind diamonds with a pointed lower part, which for the first time could reflect light incident from above back to the viewer through total reflection . Such diamonds were then set open at the bottom, and many diamond roses are said to have been cut. Like the diamond roses foiled below, this cut showed good brilliance and the fire of the diamond. Up until the 19th century, processing consisted of only two techniques, splitting along the split planes (octahedron surfaces) and grinding / polishing. With the invention of sawing, diamonds could be developed with a modern cut and with less processing loss. The modern cut was created in the 20th century, with a significantly higher light output that pushes the fire into the background.

Since the 1980s, diamonds have been processed with lasers, among other things, to remove dark inclusions and mark stones. The natural color of diamonds cannot be influenced as easily as with other gemstones. Unsightly stones have been given to irradiation in nuclear reactors to change their color since the 1960s. The result is permanent color changes. Dirty gray, white and yellowish stones are given a bright blue or green. This can be followed by a heat treatment, whereby the crystal changes generated by radiation partially “heal” again and become visible as further color changes. The results are not always clearly predictable.

Diamond determination

Diamond spectrum, figures in Ångström units

Criteria for recognizing a diamond include: a. its density, hardness, thermal conductivity, gloss, light scattering or dispersion, light refraction or refraction and the type and formation of existing inclusions.

Another important instrument to distinguish between natural and artificially colored diamonds is absorption spectroscopy . Diamonds come in a variety of colors and shades, including yellow, brown, red, and blue. The colors are mainly based on the incorporation of foreign elements (e.g. nitrogen or boron ) in the carbon lattice of natural diamonds.

Diamonds

Eppler -brillant

A particularly characteristic - and by far the most common form of cut for diamonds - is the brilliant cut. Its characteristics are at least 32 facets and the table in the upper part, a circular girdle and at least 24 facets in the lower part. Only diamonds cut in this way may be called brilliant-cut diamonds . Additional information such as real or similar is not permitted because it is misleading. The term brilliant always refers to diamonds. It is possible - and not uncommon - to process other gemstones or imitations with a brilliant cut, but these must then be clearly identified, for example as brilliant cut zirconia .

Rating of cut diamonds

To evaluate the quality and thus also the price of a cut diamond, the so-called four C criteria are used : Carat, Color, Clarity and Cut.

According to the Kimberley Process Certification Scheme, the price per carat in 2010 is between US $ 342.92 (for diamonds from Namibia) and US $ 67.34 (from Russia). However, particularly rare and high-quality specimens usually achieve extremely higher prices at auctions. On November 13, 2018, at an auction at Christie's auction house, a pink diamond called "Pink Legacy" was sold for 39.1 million euros, which set a new world record at 2.6 million dollars per carat. On April 4, 2017, the 59.6-carat "Pink Star" fetched 71.2 million dollars (approx. 67 million euros) at Sotheby’s Hong Kong. For the famous " Oppenheimer Blue ", a blue diamond with 14.62 carats and the predicate "Fancy Vivid Blue" for the rarest and most sought-after color expression in blue diamonds, at Christie's Geneva on May 19, 2016, 57 million dollars (approx Million euros) the highest bid.

Weight in carat (carat weight)

The unit of weight for gemstones is the carat, abbreviation ct . The name of this unit is derived from the Arabic or Greek name for the seeds of the carob tree (Latin: Cerat onia siliqua). These were previously used as weights. A metric carat is exactly 0.2 grams.

Purity (clarity)

The following abbreviations and technical terms are used to describe the purity (ranking), whereby the criteria relate to the assessment by a trained specialist:

Short name meaning description
fl flawless flawless even at 10x magnification (no inclusions and no external defects visible)
if internally flawless flawless except for possible surface traces from processing
vvs1 / vvsi very, very small inclusions Inclusions are very, very difficult to see even at ten times magnification.
vvs2 very, very small inclusions Inclusions are very difficult to see even at ten times magnification.
vs1 / vsi very small inclusions Inclusions are difficult to see at ten times magnification.
vs2 very small inclusions Inclusions can be seen at ten times magnification.
si1 small inclusions Inclusions are easy to see at ten times magnification.
si2 small inclusions Inclusions are very easy to see at ten times magnification, but not with the naked eye.
pi1 Piqué I (Pique I) Inclusions are barely visible to the naked eye, but do not reduce the brilliance.
pi2 Piqué II (Pique II) Inclusions visible to the naked eye, diminish the brilliance slightly
pi3 Piqué III (Pique III) Inclusions are easily recognizable with the naked eye and significantly reduce the brilliance.

Color (color)

Diamonds that appear colorless to the untrained eye can be divided into different color classes by a specialist:

No. Color class designation GIA designation
1 Very fine white + River D.
2 Very fine white River E.
3 Fine white + Top Wesselton F.
4th Fine white Top Wesselton G
5 White Wesselton H
6th Slightly tinted white + Top crystal I.
7th Slightly tinted white Top crystal J
8th Tinted white + (Crysta) K
9 Toned white Crystal L.
11 Tinted 1 Top cape M, N
12 Tinted 2 Cape O

Cut (cut)

Natural diamond in pear-shaped (pendeloque)

The cut is decisive for the fire of a diamond. One can seem lifeless while the other seemingly sparkles. The following overview according to RAL 560 A5E distinguishes between the following four quality levels:

No. Cut description
1 Very good excellent brilliance, few or only minor external features, very good proportions
2 Good good brilliance, some external features, proportions with minor deviations
3 Medium Reduced brilliance, several major external features, proportions with considerable deviations
4th Poor Brilliance significantly reduced, large and / or numerous external features, proportions with very clear deviations.

fluorescence

Fluorescence describes an evaluation criterion for cut diamonds. A diamond with low fluorescence glows slightly under UV light, with a higher fluorescence it has a strong bluish tinge. Strong fluorescence can degrade the value of white diamonds. The fluorescence of a diamond is measured on a scale:

No. fluorescence description
1 None No fluorescence whatsoever
2 Faint Very little fluorescence
3 medium Medium fluorescence
4th Strong Clear fluorescence
5 Very strong Very strong fluorescence

Conflicts (conflicts)

Rough diamonds to finance civil wars (see section Social Influences ) are outlawed and are increasingly appearing as the "fifth C" in the consciousness of the population. Rough diamonds without an indication of origin and a Kimberly certificate are largely ostracized by dealers. There is usually no proof of origin for cut diamonds.

Fancy diamonds

The name Fancy Diamonds ( English fancy "chic"), also called Fancys for short , describes colored diamonds. While most diamonds are colored, many are unattractive. The natural color of the diamond can be dominated by all tones in the range of gray, yellow, green, brown; occasionally it changes within a stone. Pure, intense colors are rare and valuable; accordingly, better prices are paid for them, some of which can be considerably above the standard for colorless diamonds. Pink diamonds are rated 50 times higher than white diamonds. Statistically speaking, there is only one “fancy” diamond on average for every 100,000 diamonds. Yellow and brown tones, which make up more than 80 percent of all colored diamonds, are not really fanatics. Canary yellow or cognac gold brown, on the other hand, are fancy colors. A large collection of colored diamonds is the Aurora Collection .

A diamond can change its color through radioactive radiation. Artificial radiation is often followed by a temperature treatment that also influences the color. In the case of artificially irradiated diamonds, the color treatment must be specified in the certificate, as they are significantly less valuable.

The color names are chosen for sales purposes: golden orange, lemon, chocolate, noir / black, electric blue. The first major fancy source was found in South Africa in 1867 . Since the 1980s, the Argyle Mine in Australia has been the most important discovery site for pink to red fancy diamonds.

There are seven fancy colors, in addition to which there are many other intermediate colors such as gold, gray or yellow-green. A different substance is responsible for the coloring:

Copy of the Tiffany diamond.
Copy of the Green Dresden .
  • Canary yellow : nitrogen is responsible for the yellow tones . The greater the nitrogen content, the more intense the yellow or green tone. The most famous and probably largest yellow diamond is the Tiffany diamond of 128.51 carats, its gross weight was 287.42 carats. Yellow is the most common color of diamonds after white and together with brown. Another famous yellow diamond is the Golden Jubilee .
  • Brown: Defects in the crystal lattice are responsible for the brown tones. The largest brown cut diamond is the Earth Star at 111.6 carats. The largest brown diamond ever found is probably the Lesotho Brown at 601 carats.
  • Blue: The element boron is responsible for the blue color of diamonds. The largest and most famous blue diamond is the allegedly cursed Hope diamond , which weighed 112.5 carats uncut and now weighs 45.52 carats when cut. In 2014, Sotheby’s in New York auctioned a teardrop-shaped blue diamond from the Rachel Lambert Mellon collection with "only" 9.75 carats (1.95 grams) for $ 32.6 million (26.3 million euros), making it the one The highest carat value ever achieved for a diamond of $ 3.35 million. The Oppenheimer Blue with 14.62 carats, classified by the Gemological Institute of America as the largest blue diamond, was auctioned off in May 2016 for a record sum of 57.5 million dollars (51.3 million euros).
  • Green: The best-known and perhaps also the largest diamond of this color is the Dresden Green Diamond with a weight of 41.0 carats (unpolished 119.5 carats) (exhibited in the Green Vault ). Green diamonds are very rare. The green color can be caused by radiation defects.
  • Red: Presumably, crystal defects are responsible for this color. The largest red diamond ever found is the Australian Red Diamond with a gross weight of 35 carats. The largest cut red diamond is the Australian Red Shield with 5.11 carats. Pure red diamonds are the rarest of all diamonds. 90 percent of the red diamonds come from the Argyle Mine in Australia. Only ten of the purple diamonds exist, the largest of which weighs 3 carats. They all came from the Argyle Mine as well. Red diamonds are the most expensive of all diamonds.
  • Pink or pink: pink diamonds are often counted among the red diamonds. Here, too, crystal impurities are responsible for the color. The largest rough diamond of this color is the Darya-i-Nur with a weight of 182 carats and a size of 41.40 × 29.50 × 12.15 mm, the largest cut diamond of the Steinmetz Pink , now Pink Star with 59.6 Karat, which went up for auction in Geneva on November 13, 2013, fetching the highest price ever ( £ 52 million ) for a stone. The stone was renamed The Pink Dream after purchase . In February 2014, Sotheby's announced in Geneva that the buyer, the stone cutter Isaac Wolf , could not afford the purchase price. Due to the agreements with the consignor, the auction house had to take possession of the stone for about 72 million US dollars . Of the 66 largest diamonds, only one is colored pink.
  • Orange A rare 14.82 carat orange diamond owned by the Gemological Institute of America fetched a record $ 35.5 million at Christie's auction on November 12, 2013 in Geneva at Christie's . As with yellow diamonds, nitrogen is responsible for the orange color.

Black diamonds

Black diamonds became popular as fashion jewelry in the 1990s. In addition to the rare, naturally occurring carbonado , which probably came to earth through meteorites , there are black diamonds that emerged from the earth alone. The best known is the 67.5 carat Black Orlov . Today black diamonds are often produced from (inferior) bright specimens by intensive neutron radiation and offered as gemstones.

Big and famous diamonds

Representation of well-known diamonds in the Nordisk Familjebok .
Great Mughal (Fig. 1)
Regent or Pitt (Fig. 2 and 11)
Florentine (Fig. 3 and 5)
Sancy (Fig. 6)
Dresden Green Diamond (Fig. 7)
Koh-i-Noor (Fig. 8 and 10)
Hope (Fig. 9)

In the following table some particularly famous diamonds are listed together with their find weight as well as place and year of discovery. The absolute size record for documented diamond finds, however, is held by a variety known as the Carbonado , the Carbonado do Sérgio , which was discovered in Brazil in 1895 and weighs 3,167 carats.

Surname Gross weight
in carats
Found year Found land comment
Cullinan 3106.7 1905 South Africa The largest rough diamond ever found was split into 105 stones. The nine largest pieces are part of the British Crown Jewels .
Sewelo (= "rare find") 1758.7 2019, April Botswana Found by the mining company Lucara, named in July 2019, not of the highest quality, sold to luxury goods manufacturer LVMH in mid-January 2020 .
Lesedi La Rona (also Lucara diamond ) 1109 2015 Botswana 2017 sold to Laurence Graff for $ 53 million
Excelsior 995.20 1893 South Africa was split into 22 stones
Star of Sierra Leone 968.90 1972 Sierra Leone was split into 17 stones
Lesotho Legend (also Letseng Diamond ) 910 2017 Letseng Mine, Mokhotlong District , Lesotho Sold for $ 40 million in March 2018 to an undisclosed bidder
Incomparable 890 1980 Congo ground 407.5 carats
"Lucara" 2 - The Constellation 813 approx. 2015 Botswana not yet cleaned, with 813 carats sold for $ 63 million (€ 55 million)
Mogul 797.5 1650 India bluish diamond; has been considered to have disappeared since 1739.
Millennium Star 777 1990 Mbuji-Mayi District , Democratic Republic of the Congo pear-shaped cut diamond weighing 204.04 ct
Woyie River 770 1945 Sierra Leone Discovered on January 6, 1945 in the Woyie River near Koidu ; was cut into 30 smaller diamonds; Victory is the largest partial diamond, weighing 31.34 carats.
Golden Jubilee 755 1985 South Africa Part of the Thai Crown Jewels. Cut 545.67 carats, making it the largest cut diamond.
President Vargas 726.8 1938 Brazil was split into 29 stones.
Jonker 726 1934 South Africa
Peace diamond 709.4 2017 Sierra Leone yellowish, solid diamond Auctioned for $ 6.5 million (€ 5.46 million) to the British jeweler Laurence Graff
Lesotho Promise 603 2006 Lesotho highest rank for color on the list of greatest diamonds, split into 26 stones
Centenary 599 July 17, 1986 Premier Mine in Cullinan (South Africa) "Colorless" diamond, color class D, cut by Gabi Tolkowsky and team in 1990/91 to 273.85 carats and 247 facets. Sold to unknown.
NN (Diavik) 552 December 16, 2018 Canada yellow, from the Diavik mine, the largest from North America
Jacob Diamond 400 1891 India since 1892 in possession of the Nizam of Hyderabad Asaf Jah VI. ; Bought by the State of India as part of the Nizam's Jewelery Trust in 1992
Oppenheimer Diamant (also Dutoitspan Diamant ) 253.7 1964 South Africa Light yellow, uncut, octahedral diamond. Named after Ernest Oppenheimer and a member of the Smithsonian Institution since 1964 .
Victoria Transvaal Diamond (also tree gold diamond ) 240 1951 South Africa Champagne-colored stone cut in the shape of a teardrop. With the Smithsonian Institution since 1977 .
Orloff 189.62 unknown, first mentioned in 1750 India in the scepter of the Russian tsar; today in the Diamond Fund Exposition in the Kremlin in Moscow
Diavik Foxfire 187.7 before 2018 Canada from the Diavik diamond mine, the second largest in North America
Koh-i-Noor 186 unknown, first mentioned in 1304 India today in the Tower of London
Florentine 137.27 unknown; Mentioned for the first time in 1477, uncertain possibly India yellow diamond; belonged to Emperor Karl I (Austria-Hungary) , sold it to Sondheimer, then probably lost to the fraudster Bruno Steiner, whereabouts unknown thereafter
Regent or Pitt 136.75 around 1700 India Part of the French Crown Jewels, kept in the Louvre
Cora Sun-Drop 110.3 unknown South Africa With 110.3 carats, it is the largest intense yellow, pear-shaped diamond
Nassak (also Nassac or Eye of the Idol ) over 90 15th century Amaragiri Mine, Mahbubnagar , Andhra Pradesh, India colorless, weight after the last triangle cut 43.38 ct; once in the Trimbakeshwar Shiva temple near Nassak, now privately owned
Shah 86 around 1450 India with an engraving of its three royal owners (one was Shah Janan, hence his name); today in the Diamond Fund Exposition in the Kremlin in Moscow
Löffelmacher Diamond (Turkish: Kasikci Elmasi , English: Spoon Maker's Diamond ) 86 unknown unknown The colorless diamond, weighing 86 carats, may have come from India and has been owned by the Turkish government and exhibited in Istanbul's Topkapı Palace since around the beginning of 1800 .
Archduke Joseph 76.02 unknown, first mentioned in 1933 India belonged to Archduke Joseph August of Austria until June 1933
Sancy 55.23 unknown, first mentioned in 1477 India Part of the French Crown Jewels, kept in the Louvre
Hope diamond 45.52 unknown, first mentioned in 1642 India blue diamond; First exposed in 1642, today on permanent loan to the National Museum of Natural History in Washington DC
Dresden Green Diamond 41 around 1722 India Apple- green color, pendulum-shaped faceted cut , today in the New Green Vault in Dresden
Blue Wittelsbacher 35.5 before 1722 India blue color, part of the crown of the Kingdom of Bavaria from 1806 to 1918

trade

Much of the uncut and cut diamonds are traded on diamond exchanges, of which there are 30 worldwide. One of the most important is based in Antwerp . The world association of diamond exchanges also resides there.

De Beers is the most important of the producers and traders and has long held a monopoly. The group was mainly controversial because of its approach of buying up surplus diamonds and thus keeping the price of diamonds stable.

The German Diamond and Gemstone Exchange is a combined exchange for both diamonds and gemstones.

Industrial diamonds make up by far the largest part of the diamond volume traded - only 3% of industrial diamonds are of natural origin. This 3% is the 70% of the natural diamonds extracted that do not meet the requirements of jewelry production.

Further use

Single crystal industrial diamond for
dressing grinding wheels

The most prestigious application is diamonds as high-quality gemstones . Non-precious diamonds that cannot be used as gem stones, fine diamond dust or industrial diamonds are referred to as "bord", although they are of far greater economic importance than jewelry diamonds .

Tools

Due to its great hardness, wear resistance and thermal conductivity in industrial production, Bort is mainly used as a cutting material , i.e. for drills , milling tools and turning tools , as well as an abrasive for grinding wheels or as an addition to polishing pastes . As a cutting material, diamond can be used as a monocrystalline diamond, which consists of a single piece. Polycrystalline diamond tools are more common in which small diamond grains have been sintered with a binder to form a larger tool . The binder is used to fill the gaps between the grains. Only granular media are used for diamond abrasives. In some areas it is extremely economical to use diamond tools, which can minimize downtime costs and tool changeover times. The required surface quality can often be achieved in one work step with the aid of diamond tools without additional processing. They are often used for the precision machining of aluminum and copper .

Diamond tools are not suitable for machining steel, as they convert to graphite at the high temperatures that occur there and the carbon atoms diffuse into the steel .

Diamond tips for glass cutters and impeder for hardness testers are also known .

Diamond-like layers

Thin CVD layers made of diamond-like carbon serve as wear protection.

By adding boron , phosphorus or nitrogen , diamond can be made conductive and function as a semiconductor or even as a superconductor . Use in electronic circuits could lead to higher switching speeds due to the high mobility of the charge carriers in the diamond single crystal and the good temperature tolerance. Electrically conductive diamond coatings can be used to manufacture electrodes for use in chemical reactions that have to withstand very reactive radicals. On an industrial scale, wastewater treatment and purification comes into focus, where CVD diamond electrodes are used for the oxidation and disinfection of e.g. B. sewage and process water are used.

The coating of silicon wafers with artificial diamond, which can be used by the semiconductor industry to achieve better cooling of electronic circuits, has already been implemented .

optics

One field of application for pure diamonds is infrared spectroscopy and the manufacture of lenses and windows.

Others

The stylus of higher quality cartridges for playing records are made of diamond. These diamonds have a special shape and sit in the aluminum or boron needle carrier.

A multitude of tiny diamonds in a free-flowing form were used in an hourglass .

Diamond anvil cells are used in materials research to achieve very high pressures in the gigapascal range.

Social influences

Diamond prospectors in Sierra Leone

While the majority of today's diamonds are mined with modern means by very few international corporations such as the De Beers company , the exorbitant price that is paid for diamonds is causing excavations among pathetic ones, especially in the underdeveloped regions and crisis areas of the world and sometimes life-threatening conditions. Even if individual miners find what they are looking for, the rough diamonds are mostly sold cheaply to the local rulers, so that only a fraction of the profits remain with the actual miners.

The profits from the diamond trade are also used to finance several civil wars on the African continent, for example in the Democratic Republic of the Congo . For this reason too, attempts are being made today to stop the trade in these blood diamonds or conflict diamonds . However, it is not very easy to tell where a diamond is, and certificates that are supposed to provide proof of origin are often forged. Today it is possible to individually mark diamonds with lasers. The origin can then be checked on the basis of this identification number.

In the illegal arms trade, especially in West Africa, paying with diamonds is not uncommon. The reasons for this are obvious: they are small (therefore easy to carry and hide), valuable, and their value hardly fluctuates. None of this is usually the case with local currencies.

Others

In 2019, a diamond was discovered within another diamond for the first time. The 5 mm large and 0.6 carat diamond contains a 6 mm 3 cavity in which a 2 mm large and 0.02 carat diamond is enclosed . It is therefore also known as the “ Matryoshka diamond” and was funded by the Russian company ALROSA in Yakutia . The age of the diamond is estimated to be around 800 million years.

See also

literature

Web links

Commons : Diamond  - collection of pictures, videos and audio files
Wiktionary: Diamant  - explanations of meanings, word origins, synonyms, translations

Individual evidence

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