Dioptase

Dioptase crystallises in stubby prismatic forms with fine striations on the faces. Its colour varies from intense green to bluish green. Its low hardness and easy cleavage make this mineral rather unsuitable for cutting. It does not melt, it does, however, dissolve in ammonia and in hydrochloric and nitric acids.

Dioptase is a rather rare mineral. It forms within copper oxidation zones.

It is often used in goldsmiths' work and for ornamental purposes.