Azurite

Chemistry: Copper carbonate.
Crystal system: Monoclinic; short dense crystals; prismatic, often as spherical radiating groups or botryoidal masses.
Color: Semi-translucent to opaque; dark blue to violetish blue; some transparent crystals.
Hardness: 3.25 - 4
Cleavage: Perfect; Fracture: conchoidal to uneven, brittle.
Specific gravity: 3.7 – 3.9
Refractive index: 1.730 – 1.838; Biaxial positive; 0.108
Luster: Vitreous to waxy
Dichroism: Light blue/dark blue
Occurrence: Secondary ore of copper; found in oxidized portions of copper veins; France, S.Africa, USA, Australia, Russia.

Notes
Unstable. Usually found in conjunction with malachite ‘azurmalachite’; tough variety is called ‘royal gem azurite’ (Las Vagas, USA); effervesces with acid (hydrochloric acid).