Lazulite

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Lazulite
Lazulite-tmix07-168a.jpg
Lazulite, Near Rapid Creek, Yukon, Canada
General
Category Phosphate mineral
Formula
(repeating unit)
(Mg,Fe2+)Al2(PO4)2(OH)2
Strunz classification 08.BB.40
Crystal symmetry Monoclinic prismatic
H-M symbol: (2/m)
Space group: P 21/c
Unit cell a = 7.144(1) Å, b = 7.278(1) Å, c = 7.228(1) Å; β = 120.5(1)°; Z=2
Identification
Color Azure-blue, sky-blue, bluish white, yellow-green, blue-green, rarely green
Crystal habit Tabular, acute to stubby bipyramidal crystals; granular, massive
Crystal system Monoclinic
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° to 70°
Fusibility Infusible
Solubility Insoluble
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, Northern Areas, 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
Lazulite from Färbergraben, Werfen, Austria. Blue crystals of lazulite to 1.2 cm on a quartz matrix.