In mineralogy, diamond is a metastable allotrope of carbon, where the carbon atoms are arranged in a variation of the face-centered cubic crystal structure called a diamond lattice. Diamond is less stable than graphite, but the conversion rate from diamond to graphite is negligible at standard conditions. Diamond is renowned as a material with superlative physical qualities, most of which originate from the strong covalent bonding between its atoms. In particular, diamond has the highest hardness and thermal conductivity of any bulk material. Those properties determine the major industrial application of diamond in cutting and polishing tools and the scientific applications in diamond knives and diamond anvil cells.

Because of its extremely rigid lattice, it can be contaminated by very few types of impurities, such as boron and nitrogen. Small amounts of defects or impurities (about one per million of lattice atoms) color diamond blue (boron), yellow (nitrogen), brown (lattice defects), green (radiation exposure), purple, pink, orange or red. Diamond also has relatively high optical dispersion (ability to disperse light of different colors).

Most natural diamonds are formed at high temperature and pressure at depths of 140 to 190 kilometers (87 to 118 mi) in the Earth's mantle. Carbon-containing minerals provide the carbon source, and the growth occurs over periods from 1 billion to 3.3 billion years (25% to 75% of the age of the Earth).

Diamonds are brought close to the Earth's surface through deep volcanic eruptions by a magma, which cools into igneous rocks known as kimberlites and lamproites. Diamonds can also be produced synthetically in a HPHT method which approximately simulates the conditions in the Earth's mantle. An alternative, and completely different growth technique is chemical vapor deposition (CVD). Several non-diamond materials, which include cubic zirconia and silicon carbide and are often called diamond simulants, resemble diamond in appearance and many properties. Special gemological techniques have been developed to distinguish natural diamonds, synthetic diamonds, and diamond simulants.

Diamonds are thought to have been first recognized and mined in India, where significant alluvial deposits of the stone could be found many centuries ago along the rivers Penner, Krishna and Godavari. Diamonds have been known in India for at least 3,000 years but most likely 6,000 years.

Diamonds have been treasured as gemstones since their use as religious icons in ancient India. Their usage in engraving tools also dates to early human history. The popularity of diamonds has risen since the 19th century because of increased supply, improved cutting and polishing techniques, growth in the world economy, and innovative and successful advertising campaigns.

In 1772, Antoine Lavoisier used a lens to concentrate the rays of the sun on a diamond in an atmosphere of oxygen, and showed that the only product of the combustion was carbon dioxide, proving that diamond is composed of carbon.

Later in 1797, Smithson Tennant repeated and expanded that experiment. By demonstrating that burning diamond and graphite releases the same amount of gas, he established the chemical equivalence of these substances.

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.

The most familiar uses of diamonds today are as gemstones used for adornment, a use which dates back into antiquity, and as industrial abrasives for cutting hard materials. The dispersion of white light into spectral colors is the primary gemological characteristic of gem diamonds.

In the 20th century, experts in gemology developed methods of grading diamonds and other gemstones based on the characteristics most important to their value as a gem. Four characteristics, known informally as the four Cs, are now commonly used as the basic descriptors of diamonds: these are carat (its weight), cut (quality of the cut is graded according to proportions, symmetry and polish), color (how close to white or colorless; for fancy diamonds how intense is its hue), and clarity (how free is it from inclusions).

Not all diamonds found on Earth originated on Earth. Primitive interstellar meteorites were found to contain carbon possibly in the form of diamond. A type of diamond called carbonado that is found in South America and Africa may have been deposited there via an asteroid impact (not formed from the impact) about 3 billion years ago. These diamonds may have formed in the intrastellar environment, but as of 2008, there was no scientific consensus on how carbonado diamonds originated.

Diamonds can also form under other naturally occurring high-pressure conditions. Very small diamonds of micrometer and nanometer sizes, known as microdiamonds or nanodiamonds respectively, have been found in meteorite impact craters. Such impact events create shock zones of high pressure and temperature suitable for diamond formation. Impact-type microdiamonds can be used as an indicator of ancient impact craters. Popigai crater in Russia may have the world's largest diamond deposit, estimated at trillions of carats, and formed by an asteroid impact.

Scientific evidence indicates that white dwarf stars have a core of crystallized carbon and oxygen nuclei. The largest of these found in the universe so far, BPM 37093, is located 50 light-years. away in the constellation Centaurus. A news release from the Harvard-Smithsonian Center for Astrophysics described the 2,500-mile (4,000 km)-wide stellar core as a diamond. Read more

Diamonds in the News ...

'Impossibly Rare' Violet Diamond Found   Discovery - May 3, 2016

A rare violet diamond, the largest of its kind ever found at Australia's remote Argyle mine, will be the centerpiece of Rio Tinto's annual pink diamonds showcase, the company said Tuesday.The rough gem, discovered in August 2015 at a mine where more than 90 percent of the world's pink and red jewels are produced, originally weighed 9.17 carats and had etchings, pits and crevices. After weeks of assessment, the Argyle Violet was polished down to a 2.83 carat, oval-shaped diamond. Diamonds for sale as part of the annual Argyle pink diamonds tender can fetch $1-2 million a carat. As a basic rule of thumb, pink and red diamonds are worth about 50 times more than white diamonds.

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 uncovered—a 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 Earth's deepest secrets. The Earth's 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.