Dioptase is an intense emerald -green to bluish-green copper. It is transparent to translucent is vitreous to sub-adamantine. Its formula is Cu6Si6O18·6H2O (also reported as CuSiO2(OH)2). It has a hardness of 5, the same as tooth enamel. Its specific gravity is 3.28–3.35, and it has two perfect and one very good cleavage directions. Additionally, dioptase is very fragile, and specimens must be handled with great care. It is a trigonal mineral, forming 6-sided crystals that are terminated by rhombohedra.
It is popular with mineral collectors and is sometimes cut into small gems. It can also be ground up and used as a pigment for painting.