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Lazulite

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Lazulite
Lazulite specimen found near Rapid Creek, Yukon, Canada
General
CategoryPhosphate mineral
Formula
(repeating unit)
(Mg,Fe2+)Al2(PO4)2(OH)2
IMA symbolLzl[1]
Strunz classification8.BB.40
Crystal systemMonoclinic
Crystal classPrismatic (2/m)
(same H–M symbol)
Space groupP21/c
Unit cella = 7.144(1), b = 7.278(1)
c = 7.228(1) [Å]; β = 120.5(1)°; Z = 2
Identification
ColorAzure, sky blue, bluish white, yellow-green, blue-green, rarely green
Crystal habitTabular, acute to stubby bipyramidal crystals; granular, massive
TwinningCommon by several twin laws
CleavagePoor to good on {110}, indistinct on {101}
FractureUneven, splintery
TenacityBrittle
Mohs scale hardness5.5–6.0
LusterVitreous
StreakWhite
DiaphaneityTransparent to translucent to nearly opaque
Specific gravity3.122–3.240
Optical propertiesBiaxial (−)
Refractive indexnα = 1.604–1.626
nβ = 1.626–1.654
nγ = 1.637–1.663
Birefringenceδ = 0.033–0.037
PleochroismStrong: X = colorless, Y = blue, Z = darker blue
2V angleMeasured: 61–70°
FusibilityInfusible
SolubilityInsoluble
References[2][3][4][5]

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 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 from Laila, Gilgit District, Gilgit-Baltistan, Pakistan. Size: 2.4 cm × 1.7 cm × 0.8 cm (0.94 in × 0.67 in × 0.31 in).

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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  1. ^ 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.
  2. ^ a b c "Lazulite" (PDF). Handbook of Mineralogy. RRUFF. Archived (PDF) from the original on Jul 5, 2021.
  3. ^ a b c d e Lazulite, Mindat.org
  4. ^ Lazulite Mineral Data, WebMineral.com
  5. ^ a b c d Hurlbut, Cornelius S.; Klein, Cornelius (1985). Manual of Mineralogy (20th ed.). Wiley. ISBN 0-471-80580-7.
  6. ^ Krivovichev V. G. Mineralogical glossary. Scientific editor A. G. Bulakh. — St.Petersburg: St.Petersburg Univ. Publ. House. 2009. — 556 p. (in Russian)
  7. ^ "Lazulite". Minerals.net.