Lazulite

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Lazulite
Lazurite, afghanite et pyrite sur calcite (Sar-e-Sang, Koksha Valley, Badakshan - Afghanistan).jpg
General
CategoryPhosphate mineral
Formula
(repeating unit)
(Mg,Fe2+)Al2(PO4)2(OH)2
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-blue, 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° to 70°
FusibilityInfusible
SolubilityInsoluble
References[1][2][3][4]

Lazulite ((Mg,Fe2+)Al2(PO4)2(OH)2)[2] is a blue, phosphate mineral containing magnesium, iron, and aluminium phosphate. Lazulite forms one endmember of a solid solution series with the darker iron rich scorzalite.[2][4]

Lazulite crystallizes in the monoclinic system. Crystal habits include steep bipyramidal or wedge-shaped crystals.[5] Lazulite has a Mohs hardness of 5.5 to 6 and a specific gravity of 3.0 to 3.1. It is infusible and insoluble.[4]

Occurrence and discovery[edit]

Lazulite: Laila, Gilgit District, Gilgit-Baltistan, Pakistan. Size 2.4 x 1.7 x 0.8 cm.

It forms by high grade metamorphism of high silica quartz 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.[1] It may be confused with lazurite, lapis lazuli or azurite.

It is 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.[2] Its name comes from the German lazurstein, for blue stone[1] or from the Arabic for heaven.[2][4]

References[edit]

  1. ^ a b c Handbook of Mineralogy
  2. ^ a b c d e Mindat.org
  3. ^ Webmineral data
  4. ^ a b c d Hurlbut, Cornelius S.; Klein, Cornelius, 1985, Manual of Mineralogy, 20th ed., Wiley, ISBN 0-471-80580-7
  5. ^ Lazulite on Minerals.net