Diamond (from the ancient Greek αδάμας – adámas “unbreakable”) is an allotrope of carbon, where the carbon atoms are arranged in a cubic crystal structure called a diamond lattice. The most common form, or habit, of diamond in nature, is the octahedron, or double pyramid shape, as seen in this photo of a rough diamond crystal, and the octahedron structures I built to demonstrate.
Diamond is renowned as a material with superlative physical qualities, such as the highest Hardness and Thermal Conductivity of any bulk material. Those properties determine the major industrial application of diamond in cutting and polishing tools and the scientific applications in diamond knives and diamond drills, and rarely as thermal insulation.
Small amounts of defects or impurities (about one per million of lattice atoms) color diamond blue (boron), yellow (nitrogen), brown (lattice defects), green (radiation exposure), purple, pink, orange or red. See Fancy Color. Here is a small sampling of the range of diamond colors:
Most natural diamonds are formed at high temperature and pressure at depths of 140 to 190 kilometers (87 to 120 mi) in the Earth’s mantle. Carbon-containing minerals provide the carbon source, and the growth occurs over periods from 1 billion to 3.3 billion years (25% to 75% of the age of the Earth). Diamonds are brought close to the Earth′s surface through deep volcanic eruptions by a magma, which cools into igneous rocks known as kimberlites and lamproites.
I founs some photos below to show the process of diamond “cutting” which is actually less “cutting” (though for larger stones this is part of the process) and is usually composed mostly of grinding and polishing the rough diamond with minute diamond dust (the only material that can scratch or polish another diamond), traditionally on a bronze wheel coated with linseed oil and diamond dust.
There is an excellent article about diamonds in Wikipedia.