Lazulite or Azure spar[6]: 14 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.[7] 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
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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, trolleite, 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
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- ^ Warr, L. N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3). Mineralogical Society of Great Britain and Ireland: 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
- ^ a b c "Lazulite" (PDF). Handbook of Mineralogy. RRUFF. Archived (PDF) from the original on Jul 5, 2021.
- ^ a b c d e Lazulite, Mindat.org
- ^ Lazulite Mineral Data, WebMineral.com
- ^ a b c d Hurlbut, Cornelius S.; Klein, Cornelius (1985). Manual of Mineralogy (20th ed.). Wiley. ISBN 0-471-80580-7.
- ^ Krivovichev V. G. Mineralogical glossary. Scientific editor A. G. Bulakh. — St.Petersburg: St.Petersburg Univ. Publ. House. 2009. — 556 p. (in Russian)
- ^ "Lazulite". Minerals.net.