An elementary substance, not metallic in its nature, which is present in all organic compounds. Atomic weight 11.97. Symbol C. it is combustible, and forms the base of lampblack and charcoal, and enters largely into mineral coals. In its pure crystallized state it constitutes the diamond, the hardest of known substances, occuring in monometric crystals like the octahedron, etc. Another modification is graphite, or blacklead, and in this it is soft, and occurs in hexagonal prisms or tables. When united with oxygen it forms carbon dioxide, commonly called carbonic acid, or carbonic oxide, according to the proportions of the oxygen; when united with hydrogen, it forms various compounds called hydrocarbons. Compare Diamond, and Graphite.
A diamond is composed of pure carbon. Carbon, when subjected to tremendous amounts of heat and pressure, crystallizes. Many diamonds do not completely crystallize. As a diamond crystal forms, some Carbon may not be crystallized resulting in birthmarks known as inclusions. Inclusions aid jewelers in identifying diamonds and make every diamond unique. The best way to identify your diamond is know what its inclusions look like, unless of course you are fortunate enough to own a flawless diamond, which has perfect crystal structure and no inclusions.