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 | |
|---|---|
 Lazulite specimen found near Rapid Creek, Yukon, Canada | |
| General | |
| Category | Phosphate mineral |
| Formula (repeating unit) | (Mg,Fe2+)Al2(PO4)2(OH)2 |
| IMA symbol | Lzl[1] |
| Strunz classification | 8.BB.40 |
| Crystal system | Monoclinic |
| Crystal class | Prismatic (2/m) (same H–M symbol) |
| Space group | P21/c |
| Unit cell | a = 7.144(1), b = 7.278(1) c = 7.228(1) [Å]; β = 120.5(1)°; Z = 2 |
| Identification | |
| Color | Azure, sky blue, bluish white, yellow-green, blue-green, rarely green |
| Crystal habit | Tabular, acute to stubby bipyramidal crystals; granular, massive |
| Twinning | Common by several twin laws |
| Cleavage | Poor to good on {110}, indistinct on {101} |
| Fracture | Uneven, splintery |
| Tenacity | Brittle |
| Mohs scale hardness | 5.5–6.0 |
| Luster | Vitreous |
| Streak | White |
| Diaphaneity | Transparent to translucent to nearly opaque |
| Specific gravity | 3.122–3.240 |
| Optical properties | Biaxial (−) |
| Refractive index | 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 angle | Measured: 61–70° |
| Fusibility | Infusible |
| Solubility | Insoluble |
| References | [2][3][4][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]
Occurrence and discovery
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 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]
References
