What does a diamond really look like?

Diamonds cannot help but fascinate. Even people who are indifferent to jewelry (yes, there are such people) are fascinated by their unimaginable beauty, born in the bowels of the earth, or even in distant galaxies. Not everyone can afford these fantastic stones, but you can admire them endlessly, like stars shining in the night. How did nature give birth to this miracle and how did it paint selected representatives of a privileged family in different colors of the rainbow?

History of origin

The chemical composition of diamond is primitive – it is the purest carbon. Much cheaper and more common substances – graphite and coal – have a similar composition. However, they have a fundamentally different crystal lattice structure, and therefore lack diamond hardness and brilliance.

Diamond is the hardest substance on Earth, taken as the starting point on the Mohs scale. Many chemists and physicists are of the opinion that it is impossible to create a more solid substance even in laboratory conditions. The only exceptions are the descendants of diamond that are modified at the molecular level.

For a long time it was believed that diamonds were born in rivers – this is where our ancestors found these stones. But a couple of centuries ago it was proven that these marvelous stones are products of fundamentally different processes occurring over hundreds of billions of years. However, debates about the nature of the origin of diamonds are still ongoing. Modern science believes that diamonds are formed in the Earth’s mantle. At a monstrous depth, in the depths of our planet, under the influence of high temperatures and incredible pressure, carbon atoms form a special cubic crystal lattice. These are diamonds. Over millions of years, during volcanic processes, future diamonds gradually rise into the earth’s crust, and sometimes are brought to the surface. Most gem-quality diamonds are mined in so-called kimberlite pipes. There are also special “impact” diamonds. According to most theories, they were formed several billion years ago as a result of a supernova explosion in a distant corner of the Galaxy and arrived on Earth along with meteorites.

Impact diamonds, although stellar in the literal sense of the word, are not distinguished by their transparency and significant size. They are usually used for technical needs.

• Jewelry diamonds. Relatively large stones that can be cut and used in the production of jewelry. These stones have a minimum of inclusions, are transparent and, after cutting, turn into diamonds.
• Industrial diamonds. Small, cloudy, damaged stones that are used for technical needs (mainly for the production of abrasives, cutting, drilling and drilling equipment)
• Board. This is essentially diamond chips. There is a jewelry bead, which is used to decorate jewelry, and a technical bead, which is used in production like other diamonds of the corresponding group.

Currently, diamond mining is carried out in more than 40 countries around the world, and the reserves of this stone are gradually depleted. The most impressive diamond reserves (of those discovered) are located in a number of African countries, Canada and Russia.

About a quarter of the world’s diamonds are mined in Russia. The largest deposits are located in Yakutia, near Arkhangelsk, in the Perm region. Most Russian diamonds are mined in Yakutia, but only 20% of them become diamonds. But the Permian deposits produce about 90% of gem-quality stones.

What color are diamonds?

A natural diamond is unsightly – a non-specialist and does not recognize its future sparkling splendor. This is a visually cloudy crystal of indeterminate color, the beauty of which is revealed only after cutting.

Every gem-quality diamond is subject to mandatory certification. It evaluates not only the color of the diamond, but also other characteristics of the mineral. There are many diamond grading systems, but the most authoritative is GIA, that is, the scale adopted by the Gemological Institute of America.

Let’s take a quick look at the main characteristics of diamonds according to the GIA:

• Clarity (purity). An ideal diamond is absolutely transparent and has no inclusions visible even under a microscope. However, perfection does not exist in nature, so the purest diamonds of natural origin can only approach ideal.
• Carat weight (weight in carats). One carat is 0,2 grams. The weight is estimated after the mineral is cut. A jewelry diamond can shrink 2-3 times, turning into a diamond. And the largest nuggets cannot be perfect at all, so they are often sawed into several parts, removing damaged areas and areas contaminated with impurities.
• Color Theoretically, absolutely transparent colorless (white diamonds) are valued the most. Any shade reduces the cost of the stone. Brown and yellow diamonds (those with nitrogen content) are rated lowest. The more intense the hue and lower the clarity, the cheaper the diamond. However, there are exceptions – “fancy” diamonds. They have rare shades (pink, blue, green and others like them) and are incredibly expensive.
• Cut (cut quality). Strictly speaking, only colorless and yellow brilliant-cut diamonds are called diamonds. Small diamonds (up to 0,29 carats) are processed mainly into 17 facets, larger ones – into 57. Cutting a diamond is very difficult (remember that we are dealing with the hardest substance on Earth), so the work of the cutter is assessed separately. Ideally, the light should play inside the stone and come out from each face in one beam, scattering with silver highlights.

Fancy diamonds have a fundamentally different cut, because their transparency is a priori less than that of white samples. A platform is left on top of the crystal to emphasize the sophistication of the color.

Color gradation of diamonds according to GIA and GOST

As mentioned above, there are many diamond certification systems. Russia has its own – GOST (TU scale), inherited from the USSR. We will not understand all the nuances; we will focus on the color characteristics of diamonds.

According to the GOST scale, the color of each diamond is assessed depending on two parameters. The first is the size of the stone (up to 0,29 carats or above this value), the second is the number of facets. Small diamonds can have 17 facets, medium and large (over 0,29 carats) – 57.

In addition to the classic round cut with 17 and 57 facets, there are a lot of fancy options: “Marquise”, “Drop”, “Heart”, “Emerald”, “Asscher”, “Trillion” and others like them. Diamonds of this cut are assessed individually, outside the generally accepted Russian classification according to GOST.

Colorless and slightly bluish diamonds are valued most highly, while deep yellow and brown ones are valued below. The GIA diamond color rating system is based on letter designations, while the Russian GOST operates with numbers. “Commercial” stones are rated at least 7 points on the Russian scale.

Here is how the color correspondence of diamonds to the GIA and GOST systems is expressed:

Diamonds of fancy colors are not evaluated according to general criteria. There are no scales for them, because every blue, red or green diamond is unique!

Diamonds: varieties and color

As mentioned above, diamonds come in different colors and shades. A pure cubic carbon crystal (diamond) is absolutely colorless, so the entire color palette of fancy diamonds is determined by the type and amount of impurities.

In theory, any admixture should reduce the cost of the stone, but this does not always happen. Incredible blue, blue, red, pink and even green diamonds are sold at auctions at Sotheby’s and Christie’s for fantastic sums measured in hundreds of thousands and sometimes millions of dollars.

Let’s look at different types of diamonds by color, find out how they got such a unique color and, of course, admire their incredible beauty.

Yellow

Non-fancy yellowish diamonds are quite inconspicuous – they are rarely distinguished by high clarity and beautiful color. They contain nitrogen, which determines the color (from slightly yellowish to brown). Low-transparent yellow and brown stones account for approximately 98% of global diamond production and are used primarily for technical needs.

Another thing is sunny yellow, lemon and orange stones formed with the participation of lithium. They are often quite large and have high transparency. Some yellow and orange diamonds are among the world’s top diamonds by market value. These are the incredible yellow “Drop of the Sun” weighing over 110 carats (over 12 million dollars), an almost fifteen-carat orange “Orange” drop-shaped, which was sold at auction for 36 million dollars and the legendary “Sancy”, the exact market value of which is unknown.

Brown

The brown color of a diamond is determined by the presence of iron atoms. This is the most common fancy shade, which is why brown diamonds are valued lower than their rarer counterparts.

Brown diamonds are extremely rarely transparent. Most are inconspicuous stones, suitable only for technical needs.

Blue and blue

Blue is a very rare and beautiful shade for a diamond. A blue diamond contains aluminum, which gives the stone a blue tint of varying degrees of intensity. And even rarer blue diamonds owe their color to boron molecules.

Among blue and blue diamonds there are many world celebrities and recognized champions in terms of value. These include the 12-carat Blue Moon (over $48 million), the stunning Wittelsbach, weighing about 35 carats and worth a fantastic $80 million, and of course, the legendary Hope.

The blue Hope Diamond, weighing 45,52 carats, is perhaps the most famous gem in the world. There are many tragedies and bloody stories associated with it. This fantastic stone is now in the collection of the Smithsonian Museum of the USA and, it seems, has “settled down”. It has never been put up for auction, so its market value is unknown, but experts estimate the value of Hope at $350 million.

Pink

Diamonds of amazing purity and a delicate pink hue, determined by boron additives, are occasionally found by miners in Australia, South Africa and Brazil. In essence, they are a type of brown diamond, but are much more expensive.

True pink diamonds are especially highly prized. Any shade, yellowish or brownish, reduces the cost of the stone. The exception is the rarest purple diamonds (hydrogen impurities), which belong to the same group.

The champions among pink diamonds are:

• “Martian Pink” (12,04 carats, $17,4 million);
• “Perfect Pink” (14,23 carats, $23 million);
• “Sweet Josephine” (16,08 carats, $28,5 million);
• “Unique Pink” (pear-shaped, 15,38 carats, $31,6 million);
• “The Little Prince” (34,5 carats, $39,3 million);
• “Pink Graff” (24,78 carats, $46 million);
• “Pink Star” (59,6 carats, $83,18 million).

Green

The green color of a diamond is the result of the addition of chlorine atoms. A rich green color (like a ripe green apple) is considered the reference color. There are vanishingly few green diamonds, and all of them cannot boast of significant size.

The most famous member of the green family is Aurora Green, weighing 5,03 carats, which was sold at auction for $16,8 million. That is, the cost of a carat of this green diamond is over 3 million dollars! This is an absolute record for value per carat.

Red

Red diamonds are extremely rare in nature. Moreover, scientists cannot understand why this stone acquires a rich red color.

Red diamonds are not large: the weight of the most impressive samples (Moussaieff, Deyoung Red, Kazanjian) is slightly more than 5 carats. But due to its exceptional rarity, a carat of such a stone costs at least $2 million.

Black

Once considered exclusively technical diamonds, the legendary black diamonds are now in growing demand. However, most black diamonds on the market today are artificially colored.

Natural samples rarely have sufficient transparency, uniformity of structure and luster, which narrows the scope of their use. The only thing that stands out is the very small “carbonados”, which are not at all amenable to processing.

However, there are exceptions to this rule, for example, the world-famous 67,5-carat “Black Orlov”, now inserted into a brooch and located in a private collection. In total, there are barely three hundred natural black diamonds of gem quality in the world, and all of them (except the above) are small.

The sparkle of the famous fancy diamonds is incredible and attractive, even if most of us can only admire it from a distance. However, the best diamonds are your own or sparkling on the woman you love. They may not be so big, but they were given with love!

When a diamond falls into the hands of a mineralogist, he saws it, splits it, and then burns it. From a layman’s point of view, especially if you multiply carats by dollars, his actions look inadequate. In fact, a dismembered and then cremated diamond provides knowledge, which ultimately has more practical benefits than admiring a diamond.

The diamond is inconspicuous, similar to a piece of emery stone or a fragment of bottle glass, rolled in a river or sea surf. It is only rolled up in the mantle melt of the Earth at depths of 150-300 km at a temperature of about 1000 ° C and a pressure of about 40 kbar.

Anatomy of a Diamond

Under an optical microscope, the shapes of crystals and their intergrowths are visible – cubes, octahedrons, dodecahedrons and more complex shapes. In reflected, oblique, transmitted, ultraviolet, combined, polarized light, the picture changes, like in a kaleidoscope. A specialist can, to a first approximation, read from them the fate of a diamond, its ontogenesis – youth, adolescence, maturity, old age.

By sending a beam of light with a known wavelength to a diamond face, you can obtain an interference pattern in the form of alternating rainbow stripes. The difference in relief heights is measured by the distance between them. The surface sculpture reflects both the final stage of diamond growth and post-growth processes. For example, dissolution during transportation of a crystal in a magmatic melt to the surface of the earth’s crust.

Photoluminescence of a diamond under ultraviolet light allows its anatomy to be seen [-]. Sectors and zones in a diamond can glow with all the colors of the rainbow – from red to purple. Under an infrared microscope, defects in the crystal structure and nitrogen impurities are visible.

Diamond surgery

Inclusions of other minerals can be found in diamonds. If they are similar in shape to the crystals of the host diamond, then, with a high probability, they were formed simultaneously with the diamond. Such inclusions are called syngenetic. Benchmarks of extremely high temperatures and pressures during diamond nucleation are inclusions of high-density crystalline modifications of silica – stishovite and coesite.

Garnet, olivine, pyroxene, graphite, sulfides, many other minerals and even gas-liquid inclusions are often found in diamonds []. The chemistry of prisoner minerals and their associations provides information about the history of the Earth’s mantle.

Inclusions are removed by splitting the diamond, sawing, grinding or simply burning it. Diamond burns easily at a temperature of 850-1000° C. The remaining ash can also tell a lot. Using isotope dating of ash residues, the age of syngenetic inclusions and, consequently, of the diamonds themselves was determined. This age ranges from 1,5 to 3,5 billion years. Young diamonds are hundreds of millions of years old.

Recently, increasing attention has been paid to the isotopic composition of carbon in diamond—the ratio of heavy (mantle) 13C and light (crustal) 12C isotopes. The presence in diamonds of light isotopes characteristic of organic compounds has given rise to a surge of hypotheses about its source and sparked discussions about the migration of carbon in the mantle and crust during the movement of continental and oceanic plates. Based on these data, planetary models of degassing of the Earth’s core during its evolution are constructed. They are involved even when discussing the controversial issue of the origin – organic or inorganic – of oil and natural gas.

Yakut Brazil

Few owners of diamond jewelry think about what type of crystal lattice their diamonds have – cubic, 8-sided octahedrons, 12-sided or even 24-sided. The shape of the crystals does not affect the consumer properties of diamonds – both of them sparkle and shimmer. But for mineralogists, the question of different crystal shapes is fundamental.

The scientific name for 12-sided diamond crystals is curved dodecahedroids. Before the discovery of kimberlite pipes at the end of the XNUMXth century, diamonds were mined from placers, first Indian, then Brazilian. Based on the location of the main find, the curved dodecahedroids were called “Brazilian” type diamonds. Later they were found in open industrial placers of the Urals and Northern Yakutia, in the basins of the Anabar and Olenek rivers and further to the east – in the lower reaches of the Lena. Now these diamonds can be found in specialized literature under another name – “Ural” type diamonds.

They have 12 faces in the form of rhombic pads, which have a spherical convex shape. Another feature is that each of the rhombic faces is refracted along a short diagonal of the rhombus, which is clearly visible in the photograph of a typical dodecahedroid [ – page 29].

Diamond cut by nature

The first researchers of dodecahedral crystals were the outstanding Russian geochemist, and then a graduate student at the University of Heidelberg, Alexander Fersman and his supervisor Viktor Goldshmidt. In 1911 they published a major monographic work “Der Diamant”.

Having studied a huge number of crystals and the smallest details of their morphology, the authors came to the conclusion that such rounded individuals are the result of surface dissolution of previously normally developing flat-faced forms of diamond crystals – octahedra and cubes, and even supplemented these conclusions with experiments on chemical etching of diamonds in potassium nitrate at temperature 800-900°C. However, this did not prevent a debate about the origin of round diamond crystals from flaring up in the 1950s, which lasted for half a century. Opponents again discussed whether diamond crystals acquired this shape due to growth or dissolution. Alexander Khokhryakov and Yuri Palyanov from Novosibirsk put an end to the dispute.

In the early 1990s, in their laboratory they simulated the processes occurring in the Earth’s mantle at ultra-high pressures and temperatures (25-55 kbar and 1370-1720 K), and dissolved diamonds in water-containing silicate melts. The resulting crystals were almost completely similar to natural round diamonds – curved dodecahedroids [Fig. ].

We were able to trace the entire series of transitions from a full-fledged cubic crystal to a rounded tetrahexahedroid in diamonds from the Anabar River placers. They are approximately the same size, but in nature or the laboratory, in order for the crystal to reach the shape of a full-fledged dodecahedroid, up to 80% of its original volume dissolves.

Diamond pyramids and craters

The dissolution of diamonds is accompanied by the appearance of flaws on their surface, the shape and location of which strictly depends on the structure of the crystal. On the faces of a typical octahedral diamond, triangular pits appear – trigons []. The faces of cubic crystals are covered with pits of regular quadrangular shape, often due to optical illusion they resemble overturned Egyptian pyramids []. When, during dissolution, the diamond loses its flat-edged shape, becomes rounded, and the surface becomes covered with a hilly relief [].

Not long ago, an unusual microrelief similar to a lunar landscape was discovered on the surface of diamonds from the northern placers of the Yakut diamond-bearing province. The figures of the lunar microrelief differ from the symmetrical figures associated with the volumetric dissolution of diamonds. They are asymmetrical, randomly arranged and in no way dependent on the crystalline structure of the diamond. This means that its origin is associated exclusively with the phase physical state of the solvent that interacted with it and completely reflects its shape. What could it be – liquid, melt or gas?

The first association that comes to mind is with gas bubbles, and, apparently, it is correct. When rising from the depths of the Earth, gas bubbles boil in the melt covering the diamond as the pressure drops. How the blood boils in a diver who emerges too quickly from the depths without decompression. Having reached a critical size of approximately 50 microns, the bubbles on the surface of the diamond collapsed or broke away from the surface of the crystal, covering the diamonds with “lunar craters.”

Diamond prices, which rose for five years after the 2008 crisis, have been steadily declining over the past six months, notes a report by leading market analyst Rapaport Group. Compared to the peak prices in the summer of 2011, diamonds weighing up to one carat fell in price by 27%, and larger diamonds by 23%. For diamonds, the pricing chain is much longer than for most other consumer goods – there are too many intermediaries. But more than half the cost of a diamond still comes from the price of the diamond from which it was cut. By the way, when cutting, about forty percent of the original diamond remains.

So the life of a diamond and its transformation into a diamond is a path of continuous losses, which is probably useful for both ordinary diamond fans and investors to know.

• Magazine “Kommersant Science” No. 2 dated 04.03.2015/29/XNUMX, page XNUMX