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). Most natural diamonds have ages between 1 billion and 3.5 billion years. Diamond also has a very high refractive index and a relatively high optical dispersion. Small numbers of defects or impurities (about one per million of lattice atoms) color diamond blue (boron), yellow (nitrogen), brown (defects), green (radiation exposure), purple, pink, orange, or red. They are also the reason that diamond anvil cells can subject materials to pressures found deep in the Earth.īecause the arrangement of atoms in diamond is extremely rigid, few types of impurity can contaminate it (two exceptions are boron and nitrogen). 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. 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. Transparent to subtransparent to translucentĭiamond is a solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic. Less often blue, green, black, translucent white, pink, violet, orange, purple, and red. Typically yellow, brown, or gray to colorless. Its lustrous faces also indicate that this crystal is from a primary deposit.
The slightly misshapen octahedral shape of this rough diamond crystal in matrix is typical of the mineral.
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