Lazulite

Chemistry: Magnesium aluminum phosphate.
Crystal system: Monoclinic; pointed pyramids; often twinned or granular masses.
Color: Transparent to translucent; medium to dark violetish blue/greenish blue; massive: translucent to opaque, often mottled with white.
Hardness: 5.5
Cleavage: Indistinct: 1 direction; Fracture: brittle, uneven to granular.
Specific gravity: 3.1 – 3.2
Refractive index: 1.62 mean; Biaxial negative; 0.03
Luster: Vitreous.
Dispersion: Low
Dichroism: Strong: colorless to dark blue
Occurrence: Granite pegmatites; Brazil, India, Madagascar, USA, Australia.

Notes
Faceted stones may look like blue apatite; translucent stones may be confused with azurite, lapis lazuli and sodalite; faceted (rare).