What is the hardest inorganic substance?

Answer 1

Diamond (carbon) is the hardest organic substance. Although carbon isn't, when it's compressed (underground, or in a volcano) it turns to diamond, which is the hardest substance. (plus, it's shiiny... @.@)

Diamonds are the hardest organic substance, measuring a 10 on the Mohs Scale of hardness, which is very high according to mineralogical terms.

Answer 2

Diamond is. (Note some recent work may indicate that Lonsdaleite a form of carbon closely related to diamond and extremely rare in nature and very hard to make may be harder. Some nano forms of boron nitride are apparently harder too)

Answer 3

Carbon nitride is one of the hardest inorganic substances, even harder than diamond. It has a complex crystal structure that gives it exceptional hardness and resistance to wear.