Diamonds in Space

Carbon's strong inclination to bond with other elements leads it to form connections with other carbon atoms when no other elements are available for lasting bonds.

This bonding between carbon atoms gives rise to various structures, including rings, chains, sheets, and cage-like formations. The focus here is on the latter two, which lead to the formation of structural carbon crystals.

As stars formed and expelled carbon into dense, hot clouds, carbon's tendency to bond with itself under high pressure sparked the creation of something spectacular: diamonds. These aren't the diamonds formed within the confines of rocky planets; these are diamonds born in space.

From: Symphony in C by Robert M. Hazen