Diamonds are minerals. They are one of two crystalline forms of the element carbon the hardest natural substance known, used as a gem and in industry.

Diamonds crystallize in the isometric system (see crystal ) commonly as transparent to translucent white, colorless, yellow, green, blue, or brown octahedrons (the familiar diamond shape). The extraordinary brilliancy of diamonds after faceting is due to their very high refractive index, which is greater than that of any other naturally occurring gemstone. In addition to the gem varieties there are bort, which is poorly crystallized or of inferior color and in fragmentary condition, and carbonado (black diamond), which is gray to black and opaque, with poor cleavage. Bort and carbonado are used as abrasives, in the cutting of diamonds, and for the cutting heads of rock drills.

Diamonds are found in alluvial (loose earthy material deposited by running water) formations and in volcanic pipes, filled for most of their length with blue ground or kimberlite, an igneous rock consisting largely of serpentine . At the surface the blue ground is weathered to a clay called yellow ground. Diamantiferous (or diamondiferous), or diamond-yielding, earth is mined both by the open-pit method and by underground mining. After being removed to the surface, it is crushed and then concentrated. Sorting is done by passing the concentrated material in a stream of water over greased tables. The diamond, being largely water repellent, sticks to the grease, but the other minerals retain a film of water, which prevents them from adhering to the grease. The diamonds are then removed from the grease, cleaned, and graded for sale.

The earliest sources of gem diamonds were India and Borneo, where they were found in river alluvium. All famous diamonds of antiquity were Indian diamonds, including the Great Mogul, the Orlov, the Koh-i-noor, and the Regent or Pitt. Other famous diamonds are the Hope (blue), Dresden (green), and Tiffany (yellow). In the early 18th cent., deposits similar to those in India were found in Brazil, mainly of carbonados, though they may have been known as early as 1670.

In 1867, a stone found in South Africa was recognized as a diamond. Within a few years, this began a wild search for diamonds, both in river diggings and inland. In 1870-71, dry diggings, including most of the celebrated mines, were discovered. Well-known South African diamond mines are the Dutoitspan, Bultfontein, De Beers, Kimberley, Jagersfontein, and Premier. Botswana, Namibia, and South Africa are now the world's major diamond-producing nations; other important countries include Australia, Russia, Brazil, Angola, Canada, Sierra Leone, Ghana, Tanzania, and Venezuela. The use of diamonds to finance African rebel groups and fuel civil strife in the 1990s led, in 2001 and 2002, to international agreements designed to certify legitimately mined diamonds.

Synthetic diamonds were successfully produced in 1955; a number of small crystals were manufactured when pure graphite mixed with a catalyst was subjected to pressure of about 1 million lb per sq in. and temperature of the order of 5,000 (3,000). Synthetic diamonds are now extensively used in industry.

The discoveries of 1870-71 in South Africa led to a great number of prospectors staking out claims and securing the diamonds by open-pit or quarry mining. The damage caused by floods and mudslides, unavoidable when there were so many different claims, was an important factor in the series of amalgamations carried on by Cecil Rhodes and Barnett Barnato . Rhodes brought about the merging of their interests in the De Beers Consolidated Mines, Ltd., which established (1889) an effective monopoly over the diamond industry. Loss of diamonds by theft was reduced through the passage of the so-called I.D.B. (Illicit Diamond Buying) Act, which limited the trade to licensed buyers and imposed penalties for the possession of uncut stones without a license. Thefts were further curtailed by the institution of compounds in which the workers live while employed by the company and which they leave only after being thoroughly searched.

Most of the major diamond producers belong to, or have cooperated with, the De Beers-led marketing cartel, formed to maintain the price of diamonds at a high level. De Beers, under Harry Oppenheimer's leadership (1957-84), maintained its dominant position in the industry by using its numerous worldwide companies to buy up new sources of diamonds and to control distribution of industrial diamonds and production of synthetic ones. In the last decades of the 20th cent., however, De Beers' hold over the unpolished diamond market decreased, and in 2000 the company announced it would end to its policy of controlling diamond prices through hoarding and shift its focus to increasing sales.

Diamonds   Wikipedia

Diamonds in the News ...

World's second-largest diamond 'found in Botswana'   BBC - November 19, 2015

The world's second-largest gem quality diamond has been discovered in Botswana, the Lucara Diamond firm says. The 1,111-carat stone was recovered from its Karowe mine, about 500km (300 miles) north of the capital, Gaborone. It is the biggest diamond to be discovered in Botswana and the largest find in more than a century. The 3,106-carat Cullinan diamond was found in South Africa in 1905 and cut into nine separate stones, many of which are in the British Crown Jewels.

Asteroid impacts on Earth make structurally bizarre diamonds   PhysOrg - November 21, 2014

Scientists have argued for half a century about the existence of a form of diamond called lonsdaleite, which is associated with impacts by meteorites and asteroids. A group of scientists based mostly at Arizona State University now show that what has been called lonsdaleite is in fact a structurally disordered form of ordinary diamond.

Pink Diamond Images

Australia unearths country's largest pink diamond   CNN - February 22, 2012

A 12.76-carat pink diamond has been unearthed in an Australian mine, the largest ever found in the country. Christened as the Argyle Pink Jubilee, the diamond was found in mining giant Rio Tinto's Argyle diamond mine in Western Australia's East Kimberly region. The Argyle mine is the world's largest producer of pink diamonds, with Rio Tinto reporting that the mine generates more than 90% of the global market supply. "A diamond of this caliber is unprecedented - it has taken 26 years of Argyle production to unearth this stone, and we may never see one like this again," said Argyle Pink Diamonds Manager Josephine Johnson in a statement.

Space diamonds reveal supernova origins   PhysOrg - February 15, 2012

Space diamonds may now be an astrophysicist's best friend. For years, scientists have found DNA-sized diamonds in meteorites on Earth. New research suggests that these diamonds spring from violent cosmic collisions, which may help scientists unravel mysteries surrounding exploding stars -- the birthplaces of ancient materials that predate our solar system. Although diamonds are rare on Earth, scientists believe that minuscule "nanodiamonds" abound in space. Researchers have been trying to decipher the origin of these enigmatic minerals for decades.

Vibration rocks for entangled diamonds   PhysOrg - December 16, 2011

You can take two diamonds - not quite everyday objects, but at least simple and recognizable - and put them in such a state: in particular a superposition of a state of one diamond vibrating and the other not, and vice versa.

Two Diamonds Linked by Strange Quantum Entanglement   Live Science - December 1, 2011
Scientists have linked two diamonds in a mysterious process called entanglement that is normally only seen on the quantum scale. Entanglement is so weird that Einstein dubbed it "spooky action at a distance." It's a strange effect where one object gets connected to another so that even if they are separated by large distances, an action performed on one will affect the other. Entanglement usually occurs with subatomic particles, and was predicted by the theory of quantum mechanics, which governs the realm of the very small. But now physicists have succeeded in entangling two macroscopic diamonds, demonstrating that quantum mechanical effects are not limited to the microscopic scale.

Crystals in meteorite harder than diamonds   MSNBC - February 2, 2010
Researchers using a diamond paste to polish a slice of meteorite stumbled onto something remarkable: crystals in the rock that are harder than diamonds. A closer look with an array of instruments revealed two totally new kinds of naturally occurring carbon, which are harder than the diamonds formed inside the Earth. The discovery was accidental but we were sure that looking in these meteorites would lead to new findings on the carbon system. The researchers were polishing a slice of the carbon-rich Havero meteorite that fell to Earth in Finland in 1971. When they then studied the polished surface they discovered carbon-loaded spots that were raised well above the rest of the surface - suggesting that these areas were harder than the diamonds used in the polishing paste.

  South Africa: Giant Diamond Found - 557 karats - worth 20 million $   National Geographic - October 3, 2009
Miners in South Africa recently found what may be one of the 20 largest diamonds ever uncoveredÑa 507.55-carat gem from the storied Cullinan Mine, which also produced the world's biggest diamond.

Diamonds show how Earth is recycled PhysOrg - July 30, 2008
Tiny minerals found inside diamonds have provided us with a rare glimpse of the EarthÕs deepest secrets. The EarthÕs crust that underlies our oceans is constantly being made at mid-oceanic ridges which run down the centre of our oceans. There, magma derived from the mantle (the layer beneath the crust) is injected between diverging tectonic plates, pushing them apart. On the far side of each plate, old oceanic crust is eventually recycled by returning it to the mantle at subduction zones, huge trenches that dive deep beneath the continents.

Diamonds may hold clue to origins of life MSNBC - July 28, 2008

One of the greatest mysteries in science is how life began. Now one group of researchers says diamonds may have been life's best friend. Scientists have long theorized that life on Earth got going in a primordial soup of precursor chemicals. But nobody knows how these simple amino acids, known to be the building blocks of life, were assembled into complex polymers needed as a platform for genesis. Diamonds are crystallized forms of carbon that predate the oldest known life on the planet. In lab experiments aimed to confirm work done more than three decades ago, researchers found that when treated with hydrogen, natural diamonds formed crystalline layers of water on the surface. Water is essential for life as we know it. Also, the tests found electrical conductivity that could have been key to forcing chemical reactions needed to generate the first life. When primitive molecules landed a few billion years ago on the surface of these hydrogenated diamonds in the atmosphere of early Earth, the resulting reaction may have been sufficient enough to generate more complex organic molecules that eventually gave rise to life, the researchers say.

Why Hope Diamond Has Fiery Red Phosphorescence After Exposure To Ultraviolet Light Science Daily - January 4, 2008
Shine a white light on the Hope Diamond and it will dazzle you with the brilliance of an amazing blue diamond. Shine an ultraviolet light on the Hope Diamond and the gem will glow red-orange for about five minutes. This phosphorescent property of blue diamonds can distinguish synthetic and altered diamonds from the real thing, and it may also provide a way to fingerprint individual blue diamonds for identification purposes, according to a team of researchers from the Naval Research Laboratory, the Smithsonian Institution and Penn State.

Diamonds Nearly as Old as Earth Live Science - August 23, 2007
Diamonds are indeed forever, or at least nearly as old as the Earth, a new study shows. Scientists have unearthed diamonds more than 4 billion years old and trapped inside crystals of zircon in the Jack Hills region in Western Australia. Nearly as old as Earth itself and considered the oldest terrestrial diamonds ever discovered, the gems could give insights into the early evolution of our planet's crust.

South Africa: Diamond firm finds egg-sized gem Reuters - April 22, 2006

A small diamond company uncovered a huge 235-carat gem - the size of a hen's egg - in South Africa only a few weeks after launching its operations, the firm said on Friday. Nare Diamonds Ltd. said it uncovered the rough gem on Wednesday after resuming mining in March at the Schmidtsdrift mine, 50 miles northwest of the country's historic diamond center of Kimberley. The mine was shut down three years ago by another firm that went bankrupt, a spokesman said. During the mine's previous operations, the average size of stones was 1.14 carats. "The large-sized gemstone is octahedron in shape and of very good quality according to a third party assessor," the statement to the London stock exchange said.

It is hard to set a value for the diamond because typical valuation measures fall away when diamonds reach a certain size, the spokesman said. London-listed Lonrho Africa Ltd, which recently bought a 17 percent stake in unlisted Nare, issued the statement. Its shares shot up 7.5 percent to 28-3/4 pence by 1330 GMT (9:30 a.m. EDT).The world's biggest diamond group, De Beers, found a 316.7 carat diamond at its South African Venetia mine in January, the largest-ever find at Venetia.

The largest-ever gem, the Cullinan, weighed in at 3,106 carats when De Beers discovered it in 1905, but other massive diamonds have ranged around 600-900 carats.In 1986, De Beers discovered the 755.5-carat Golden Jubilee, which is now the world's largest polished diamond at just over 545 carats. A spokesman for Nare said the discovery does not necessarily mean the mine holds other sizable gems since it is from an alluvial deposit -- a former river bed where diamonds were swept from a smattering of other eroded deposits.

Diamond star thrills astronomers BBC - February 2004

Twinkling in the sky is a diamond star of 10 billion trillion trillion carats, astronomers have discovered. The cosmic diamond is a chunk of crystallised carbon, 4,000 km across, some 50 light-years from the Earth in the constellation Centaurus. It's the compressed heart of an old star that was once bright like our Sun but has since faded and shrunk. Astronomers have decided to call the star "Lucy" after the Beatles song, Lucy in the Sky with Diamonds.

Diamond origin 'can be determined' BBC - July 25, 2003

Belgian scientists have found a way of determining the origin of individual diamonds, according to the Diamond High Council of Antwerp. The body which controls trade in diamonds says the discovery could help the worldwide campaign to stop the illegal sale of stones from war zones, a trade that has helped finance several African civil wars. The researchers found they could gain a unique chemical image of each diamond, by drilling a tiny hole in it with a laser beam. This allowed them to identify the source from which it came because each precious stone has a chemical composition specific to an individual mine.