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| 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 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). Natural and synthetic diamonds are most commonly distinguished using optical techniques or thermal conductivity measurements.
- ^ Warr LN (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. ISSN 0026-461X. S2CID 235729616.
- ^ Cite error: The named reference
mindatwas invoked but never defined (see the help page). - ^ "Diamond". WebMineral. Archived from the original on January 7, 2019. Retrieved July 7, 2009.