Diamond

Natural history

The formation of natural diamond requires very specific conditions-exposure of carbon-bearing materials to high pressure, ranging approximately between 45 and 60 kilobars (4.5 and 6 GPa, but at a comparatively low temperature range between approximately 900–1300 °C. These conditions are met in two places on Earth; in the lithospheric mantle below relatively stable continental plates, and at the site of a meteorite strike. How the diamond process made can view in interesting video" How Make Diamond".

Diamonds are formed over a period of a billion or more years deep within earth’s crust – about 150km (90 miles) deep – and is pushed to the surface by volcanoes. Most diamonds are found in volcanic rock, called Kimberlite, or in the sea after having been carried away by rivers when they were pushed to the surface.

Material Properties

A diamond is a transparent crystal of tetrahedrally carbon atoms (sp3) that crystallizes into the diamond lattice which is a variation of the face centered cubic structure. Diamonds have been adapted for many uses because of the material's exceptional physical characteristics. Most notable are its extreme hardness and thermal conductivity (900–2,320 W·m⁻¹·K⁻¹), as well as wide bandgap and high optical dispersion. Above 1,700°C (1,973 K / 3,583 °F) in vacuum or oxygen-free atmosphere, diamond converts to graphite; in air, transformation starts at ~700 °C. Diamond's ignition point is 720 - 800 °C in oxygen and 850 - 1,000 °C in air. Naturally occurring diamonds have a density ranging from 3.15–3.53 g/cm³, with pure diamond close to 3.52 g/cm³. The chemical bonds that hold the carbon atoms in diamonds together are weaker than those in graphite. In diamonds, the bonds form an inflexible three-dimensional lattice, whereas in graphite, the atoms are tightly bonded into sheets, which can slide easily over one another, making the overall structure weaker.

Theoretically predicted phase diagram of carbon                       

Diamond and graphite are two allotropes of carbon:                                                             pure forms of the same element that differ in structure.

The largest diamond

The world’s largest diamond was the Cullinan, found in South Africa in 1905. It weighed 3,106.75 carats uncut. It was cut into the Great Star of Africa, weighing 530.2 carats, the Lesser Star of Africa, which weighs 317.40 carats, and 104 other diamonds of nearly flawless color and clarity. They now form part of the British crown jewels.

The Cullinan was three times the size of the next largest diamond, the Excelsior, which was also found in South Africa. The world’s largest documented polished diamond – unearthed in 1986, also in South Africa – is called Unnamed Brown. It weighs 545 carats and was cut down from a 700 carat rough diamond. It took an international team of expert cutters 3 years to complete the masterpiece. Another impressive diamond that also took 3 years to cut, and also is part of the British crown jewels, is the Centenary Diamond. It weighs 273.85 carats and is the world’s largest flawless diamond.

The biggest diamond in the entire universe is thought to be Lucy, a crystallized white dwarf star, a star consisting of diamonds. It’s weight is 10 billion trillion trillion carat. Named after the Beatles song, Lucy in the Sky with Diamonds, it is technically known as BPM 37093.

Diamond colors

Not all diamonds are white. Impurities lend diamonds a shade of blue, red, orange, yellow, green and even black. Vivid blue, green and pink mined diamonds are the rarest. They are not the rarest gemstones, however. That title goes to a pure red ruby. Diamonds actually are found in abundance; thousands are mined every year. 80% of them are not suitable for jewelery – they are used in industry or in cheap rings.

Synthetic diamonds

Late in the 19th century, Scottish scientist  James Ballantyne Hannay mixed lithium with bone oil and paraffin, sealed it in iron tubes and heated it to red hot. He claimed, in 1879, the resultant stones were diamonds. They were stored away and only many years later they were found to be diamonds, albeit synthetic. In 1892, Henri Moissan theorized that diamonds could be synthesized by crystallizing carbon under pressure. Today, synthetic diamonds is big business, outselling mined diamonds by far. Sometimes called cubic zirconia and synthetic moissanite, they are categorized and evaluated with the same grading scale process as mined diamonds but sell for much less. Synthetic moissanite is a diamond simulant with similar thermal characteristics to mined diamonds and most people, even so-called experts, can’t tell them apart.

Weighing diamonds

A diamond carat differs from a gold carat. The gold carat indicates purity – pure gold being 24 carats. One diamond carat, for mined or synthetics diamonds, is 200 milligrams (0.007055 oz). The word carat derives from the carob bean. Gem dealers used to balance their scales with carob beans because these beans all have same weight.

Lucy, the biggest diamond in the universe 2 485 miles (4000 km) across, 10 billion trillion trillion carat

The colorless Cullinan, the biggest diamond ever found on earth, weighed 0,62kg (one and a quarter pound) uncut - it can be replicated easily synthetically

The tradition of a diamond engagement ring started in 1477 when Archduke Maximillian of Austria gave a diamond ring to Mary of Burgundy. The modern tradition is the result of a clever advertising campaign designed by N.W.Ayer in the 1940s, a marketing gimmick still used today. The fact is that most diamonds have little resale or investment value. Diamonds also cause the death of millions of innocent people.