Lazulite is a transparent to semi-opaque, blue mineral that is a phosphate of magnesium, iron, and aluminium, with the chemical formula (Mg,Fe2+)Al2(PO4)2(OH)2.[3] Lazulite forms one endmember of a solid solution series with the darker, iron-rich scorzalite.[3][5]
Lazulite crystallizes in the monoclinic system. Its crystal habits include steep bipyramidal or wedge-shaped crystals.[6] Lazulite has a Mohs hardness of 5.5–6.0 and a specific gravity of 3.0–3.1. It is infusible and insoluble.[5]
Lazulite forms by high-grade metamorphism of silica-rich rocks and in pegmatites. It occurs in association with quartz, andalusite, rutile, kyanite, corundum, muscovite, pyrophyllite,dumortierite, wagnerite, svanbergite and berlinite in metamorphic terrains; and with albite, quartz, muscovite, tourmaline and beryl in pegmatites.[2]It may be confused with lazurite, lapis lazuli or azurite.
The type locality is in Freßnitzgraben in Krieglach, it's also found in Salzburg, Austria; Zermatt, Switzerland; Minas Gerais, Brazil; Lincoln County, Georgia; Inyo County, California; the Yukon in Canada; and elsewhere.
It was first described in 1795 for deposits in Styria, Austria.[3] Its name comes from the German lazurstein, for 'blue stone'[2] or from the Arabic for heaven.[3][5]