Carbon possesses physical and chemical properties. Carbon is a non-metal that is a soft, gray substance that a person can rub between the fingernails. The element can appear jet black as well. Carbon forms the allotropes graphite, diamond and coal (amorphous). There are thousands of carbon compounds that are essential to organic life.
As graphite, the density of carbon is 2.267 grams per milliliter. Graphite sinks in water and burns to form carbon dioxide or carbon monoxide if the oxygen supply is limited. As a diamond, carbon is one of the hardest substances on Earth. Diamonds have a high melting point and point of refraction. The density of a diamond is 3.51 g/cm³. Diamonds are used for jewelry, bearings, cutting and drilling.
Elemental carbon is an inert substance. The element is insoluble in water; diluted acids and bases; and organic solvents. The only halogen to react with carbon is fluorine. Several metals combine with carbon at high temperatures to create carbides. Seven natural isotopes exist for carbon. Carbon-12 is used as the standard for atomic weights. The melting point of carbon is 3820 Kelvin, and it boils at 5100 Kelvin. Carbon has a diagonal lattice structure and a hexagonal crystal structure. It forms three gaseous compounds with oxygen: carbon monoxide, carbon dioxide and carbon suboxide.