Dioptase

Chemistry: Hydrous copper silicate
Crystal system: Trigonal
Color: Translucent to opaque; intense greenish blue
Hardness: 5
Cleavage: Perfect: 3 directions; Fracture: conchoidal to uneven.
Specific gravity: 3.28 – 3.35
Refractive index: 1.694 – 1.709; Uniaxial positive; 0.053
Luster: Vitreous.
Dispersion: High
Dichroism: -
Occurrence: Chile, Namibia, Russia, DR Congo, USA.

Notes
Attractive emerald green color; uncut crystal clusters may be set in jewelry; faceted, cabochon.