Carbon a streak on paper (hence its name, from the Greek verb "γράφειν" which means "to write"), while diamond is the hardest naturally occurring material known. Graphite is a good electrical conductor while diamond has a low electrical conductivity. Under normal conditions, diamond, carbon nanotubes, and graphene have the highest thermal conductivities of all known materials. All carbon allotropes are solids under normal conditions, with graphite being the most thermodynamically stable form at standard temperature and pressure. They are chemically resistant and require high temperature to react even with oxygen. The most common oxidation state of carbon in inorganic compounds is
Material properties of diamond ("proper", "unalterable", "unbreakable") and sometimes called adamant, diamond is the hardest known naturally occurring material, scoring 10 on the Mohs scale of mineral hardness. Diamond is extremely strong owing to the structure of its carbon atoms, where each carbon atom has four neighbors joined to it with covalent bonds. The material boron nitride, when in a form structurally identical to diamond (zincblende structure), is nearly as hard as diamond; a currently hypothetical material, beta carbon nitride, may also be as hard or harder in one form. It has been shown that some diamond aggregates having nanometer grain size are harder