Diamond: meaning, formation, treatments, lab-grown stones and care

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Diamond is carbon crystallised deep underground, the hardest natural material yet also brittle. Formation, history, treatments, synthetics, ethics and care.

Key points

Colour	colourless to yellowish most often; fancy colours: yellow, brown, pink, blue, green, black
Mineral family	native element: pure carbon (C), cubic 'diamond' structure
Hardness (Mohs)	10, but brittle: it has cleavage planes
Formation	most often at 150-250 km depth in the Earth's mantle
Age	generally between 1 and 3.5 billion years
Origin of the name	Greek adamas, 'invincible'
Earliest deposits	India, known for at least 3,000 years
Treatments and substitutes	high-pressure heating, irradiation, fracture filling; moissanite, zirconia, glass

What is diamond?

Diamond is a crystalline form of pure carbon (C), in which each atom is bonded to four neighbours in a very rigid cubic lattice. Pencil graphite is also carbon, but arranged in layers: that structure makes all the difference. At ordinary temperature and pressure, graphite is the more stable form; diamond is not 'forever' in the strict sense, but it changes so slowly that it can be ignored.

Most gem-quality diamonds formed at 150-250 km depth in the Earth's mantle, 1 to 3.5 billion years ago, before being carried up to the surface by deep volcanic eruptions, in rocks called kimberlites. A few come from much greater depths, down to 800 km.

The name comes from the Greek adamas, 'invincible' or 'unalterable'.

Historical milestones

India: diamonds were collected from the alluvial gravels of several rivers for at least 3,000 years, and perhaps 6,000 according to some authors.
19th century: the discoveries in South Africa (the Kimberley region) transform world production.
1905: at the Premier mine in South Africa, the Cullinan is found, the largest rough diamond ever discovered (3,106 carats, or 621 g). It was cut into nine major stones and 96 smaller ones; the two largest are part of the British Crown Jewels.
2003: the Kimberley Process is set up, certifying the origin of rough diamonds to limit the trade in 'conflict diamonds'.
Today: lab-grown diamonds, produced in a laboratory, hold a growing share of the market.

Traditional symbolism

Because of its hardness, diamond has been linked with invincibility, purity, constancy and clarity. Its brilliance, which reflects light like a star, has also associated it with the sun and with power. In Western tradition, it is the birthstone for April (see birthstones) and the stone for the 60th wedding anniversary.

These ideas are cultural symbols. The 'engagement diamond' as a widespread custom is in fact quite recent and owes much to 20th-century advertising campaigns. No effect on health or luck has been demonstrated.

Traditional correspondences

Area	Cited correspondence
Chakra	crown (crown chakra)
Element	air or light
Signs	Aries, Taurus, Libra (depending on the authors)
Keywords	clarity, purity, constancy

For the associated chakra, see the crown chakra.

Hard, but brittle

A diamond scratches every other mineral (10 on the Mohs scale), but it is not an unbreakable material. It has four cleavage planes: a well-placed blow can split it. Hardness (resistance to scratching) is one thing; toughness (resistance to impact) is another. Rings should therefore be worn in a protective setting, and jewellery should be removed for heavy work.

Its very high thermal conductivity is used to identify it: a diamond 'feels cold' quickly against the skin and responds to a thermal tester. But a common tester can be fooled by moissanite, which also conducts heat well.

Treatments, synthetics and imitations

Product	What it is	Good to know
Treated natural diamond	natural diamond whose colour or clarity has been altered (high-pressure heating, irradiation, fracture filling)	must be disclosed; filled stones need more care
Synthetic diamond	a real diamond, made artificially (high pressure and high temperature, or chemical vapour deposition)	same composition and hardness; must be sold as 'synthetic' or 'lab-grown'
Moissanite	silicon carbide (see carborundum)	more coloured flashes; hard (9 to 9.5)
Cubic zirconia, glass, white sapphire	other materials	softer or heavier

The question is not whether a lab-grown stone is 'real' (it is crystallised carbon, like the other) but whether the seller discloses it honestly. For a high-value diamond, ask for a certificate from a recognised gemmological laboratory.

Ethics and provenance

The Kimberley Process, created in 2003, certifies the origin of rough diamonds so that they do not fund rebel movements. It has reduced the share of 'conflict diamonds' to less than 1% of production according to Wikipedia, but it is criticised: its scope is narrow (it does not cover other human rights abuses), independent oversight is weak, and certificates are sometimes hard to enforce. Organisations such as Global Witness have left it.

To reduce the risks, ask for traceability (country of extraction, mining company), or consider a lab-grown or pre-owned (second-hand) diamond.

Care and choice

Cleaning: lukewarm water, a few drops of washing-up liquid, a very soft brush, then rinse. Ultrasonic cleaners suit untreated diamonds; avoid them for stones treated by fracture filling.
Grease: diamond attracts oily substances, which dull its brilliance. Regular cleaning keeps it sparkling.
Knocks: remove the jewellery for sport or gardening.
Sun, salt, smoke: no effect on the stone.
Choice: a diamond is graded by the '4 Cs' (carat weight, colour, clarity, cut). Prices vary enormously. A rough diamond or a small stone can be a more affordable choice. To compare with other sparkling stones, see Herkimer diamond (quartz, much less expensive) or moldavite.