Diamond Crystallization - Macle Twin

Diamonds are fascinating, hard, brilliant and impervious to acid.
Diamonds form as cubes and octohedrons. Damonds also show off a form of twinning called "Spinel" twinning, which makes the crystal take the shape that forms triangular shapes on both ends. If those triangular shaped ends get separated, they can form into a beautiful triangular diamond, like the one photographed above. That crystal is 1.8 cm across and sold in 2010 to a private collector.