In graphite the bonds are sp 2 orbital hybrids and the atoms form in planes, with each bound to three nearest neighbors 120 degrees apart. The two most common allotropes of pure carbon are diamond and graphite. Solid carbon comes in different forms known as allotropes depending on the type of chemical bond. Main article: Material properties of diamondĭiamond is a solid form of pure carbon with its atoms arranged in a crystal. Natural, synthetic and imitation diamonds are most commonly distinguished using optical techniques or thermal conductivity measurements. Imitation diamonds can also be made out of materials such as cubic zirconia and silicon carbide. Synthetic diamonds can be grown from high-purity carbon under high pressures and temperatures or from hydrocarbon gases by chemical vapor deposition (CVD). 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. Under high pressure and temperature, carbon-containing fluids dissolved various minerals and replaced them with diamonds. 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. At room temperature and pressure, another solid form of carbon known as graphite is the chemically stable form of carbon, but diamond converts to it extremely slowly. 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.

White vinyl lattice