Diamond

Diamond
A natural diamond crystal
General
Category	Native minerals
Formula (repeating unit)	C
IMA symbol	Dia[1]
Strunz classification	1.CB.10a
Dana classification	1.3.6.1
Crystal system	Cubic
Crystal class	Hexoctahedral (m3m) H-M symbol: (4/m 3 2/m)
Space group	Fd3m (No. 227)
Structure
Jmol (3D)	Interactive image
SMILES C1(C2(C7))C3(C89)C(C4(C0))C5CC1C(C1)C(C5(C5))C36C3(C21)C(C78)C(C1)C(C90)C6(C54)CC1C3 (SMILES input only shows in Preview. SMILES is used to create the Jmol 3D image.)
Identification
Formula mass	12.01 g/mol
Color	Typically yellow, brown, or gray to colorless. Less often blue, green, black, translucent white, pink, violet, orange, purple, and red.
Crystal habit	Octahedral
Twinning	Spinel law common (yielding "macle")
Cleavage	111 (perfect in four directions)
Fracture	Irregular/Uneven
Mohs scale hardness	10 (defining mineral)
Luster	Adamantine
Streak	Colorless
Diaphaneity	Transparent to subtransparent to translucent
Specific gravity	3.52±0.01
Density	3.5–3.53 g/cm3 3500–3530 kg/m3
Polish luster	Adamantine
Optical properties	Isotropic
Refractive index	2.418 (at 500 nm)
Birefringence	None
Pleochroism	None
Dispersion	0.044
Melting point	Pressure dependent
References	[2][3]

Diamond is a solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic. Diamond as a form of carbon is a tasteless, odourless, strong, brittle solid, colourless in pure form, a poor conductor of electricity, and insoluble in water. Another solid form of carbon known as graphite is the chemically stable form of carbon at room temperature and pressure, but diamond is metastable and converts to it at a negligible rate under those conditions. Diamond has the highest hardness and thermal conductivity of any natural material, properties that are used in major industrial applications such as cutting and polishing tools. They are also the reason that diamond anvil cells can subject materials to pressures found deep in the Earth.

Because the arrangement of atoms in diamond is extremely rigid, few types of impurity can contaminate it (two exceptions are boron and nitrogen). Small numbers of defects or impurities (about one per million of lattice atoms) can color a diamond blue (boron), yellow (nitrogen), brown (defects), green (radiation exposure), purple, pink, orange, or red. Diamond also has a very high refractive index and a relatively high optical dispersion.

Most natural diamonds have ages between 1 billion and 3.5 billion years. Most were formed at depths between 150 and 250 kilometres (93 and 155 mi) in the Earth's mantle, although a few have come from as deep as 800 kilometres (500 mi). Under high pressure and temperature, carbon-containing fluids dissolved various minerals and replaced them with diamonds. Much more recently (hundreds to tens of million years ago), they were carried to the surface in volcanic eruptions and deposited in igneous rocks known as kimberlites and lamproites.

Synthetic diamonds can be grown from high-purity carbon under high pressures and temperatures or from hydrocarbon gases by chemical vapor deposition (CVD). Imitation diamonds can also be made out of materials such as cubic zirconia and silicon carbide. Natural, synthetic, and imitation diamonds are most commonly distinguished using optical techniques or thermal conductivity measurements.