## diamond

https://doi.org/10.1351/goldbook.D01671
An allotropic form of the element @C00821@ with cubic structure (space group $$O_{h}^{7}- Fd3m$$) which is thermodynamically @S05900@ at pressures above $$6\ \text{GPa}$$ at room temperature and @M03872@ at atmospheric pressure. At low pressures diamond converts rapidly to @G02684@ at temperatures above $$1900\ \text{K}$$ in an @I03026@ atmosphere. The chemical bonding between the carbon atoms is covalent with $$\mathrm{sp}^{3}$$ @H02874@.
Note:
There is also a hexagonal diamond-like structure of the element carbon (lonsdaleite).
Source:
PAC, 1995, 67, 473. (Recommended terminology for the description of carbon as a solid (IUPAC Recommendations 1995)) on page 487 [Terms] [Paper]