| Lazulite | |
| Category: | Phosphate mineral |
| Imasymbol: | Lzl[1] |
| Strunz: | 8.BB.40 |
| System: | Monoclinic |
| Class: | Prismatic (2/m) (same H–M symbol) |
| Symmetry: | P21/c |
| Unit Cell: | a = 7.144(1), b = 7.278(1) c = 7.228(1) [Å]; β = 120.5(1)°; Z = 2 |
| Color: | Azure, sky blue, bluish white, yellow-green, blue-green, rarely green |
| Habit: | Tabular, acute to stubby bipyramidal crystals; granular, massive |
| Twinning: | Common by several twin laws |
| Cleavage: | Poor to good on, indistinct on |
| Fracture: | Uneven, splintery |
| Tenacity: | Brittle |
| Mohs: | 5.5–6.0 |
| Luster: | Vitreous |
| Streak: | White |
| Diaphaneity: | Transparent to translucent to nearly opaque |
| Gravity: | 3.122–3.240 |
| Opticalprop: | Biaxial (−) |
| Refractive: | nα = 1.604–1.626 nβ = 1.626–1.654 nγ = 1.637–1.663 |
| Birefringence: | δ = 0.033–0.037 |
| Pleochroism: | Strong: X = colorless, Y = blue, Z = darker blue |
| 2V: | Measured: 61–70° |
| Fusibility: | Infusible |
| Solubility: | Insoluble |
Lazulite is a transparent to semi-opaque, blue mineral that is a phosphate of magnesium, iron, and aluminium, with the chemical formula . Lazulite forms one endmember of a solid solution series with the darker, iron-rich scorzalite.
Lazulite crystallizes in the monoclinic system. Its crystal habits include steep bipyramidal or wedge-shaped crystals.[2] Lazulite has a Mohs hardness of 5.5–6.0 and a specific gravity of 3.0–3.1. It is infusible and insoluble.[3]
Lazulite forms by high-grade metamorphism of silica-rich rocks and in pegmatites. It occurs inassociation with quartz, andalusite, rutile, kyanite, corundum, muscovite, pyrophyllite,dumortierite, wagnerite, svanbergite, trolleite, and berlinite in metamorphic terrains; and with albite, quartz, muscovite, tourmaline and beryl in pegmatites.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. Its name comes from the German German: lazurstein, for 'blue stone'[4] or from the Arabic for heaven.[3]