
Diamonds typically crystallize in the face-centered cubic crystal system (space group ) and consist of tetrahedrally bonded carbon atoms. The unit cell of diamond has a two atom basis at (0,0,0) and (1/4,1/4,1/4), which means half of the atoms are at lattice points and the other half are offset by (1/4,1/4,1/4), where 1 is the length of a side of the unit cell. Diamond's density is 3.52 g·cm−3.
The tetrahedral arrangement of atoms is the source of many of diamond’s properties. The carbon atoms in Graphite, the other major allotrope of carbon, display a different (nontetrahedral) connectivity and as a result shows dramatically different physical characteristics: graphite is a soft, dark gray, opaque mineral. Other elements of the carbon group such as silicon crystalize like diamond.