Glauberite

Glauberite
Glauberite crystal group from the Bertram Siding Sulfate deposit, Imperial County, California
General
Category Sulfate minerals, anhydrous sulfate subgroup
Formula
(repeating unit)		 Na2Ca(SO4)2
Strunz classification 7.AD.25
Crystal system Monoclinic
Crystal class Prismatic (2/m)
(same H-M symbol)
Space group C2/c
Unit cell a = 10.129, b = 8.306
c = 8.533 [Å]; β = 112.19°; Z = 4
Identification
Color Gray or pale yellow, colorless
Crystal habit Tabular prismatic crystals
Cleavage Perfect on {001}, imperfect on {110}
Fracture Conchoidal
Tenacity Brittle
Mohs scale hardness 2.5 - 3
Luster Vitreous to waxy, pearly on cleavages
Streak White
Diaphaneity Transparent to translucent
Specific gravity 2.75–2.85
Optical properties Biaxial (-)
Refractive index nα = 1.507 - 1.515 nβ = 1.527 - 1.535 nγ = 1.529 - 1.536
Birefringence δ = 0.022
2V angle 24° to 34°
Dispersion strong r > v
Solubility HCl and H2O (water) soluble
Alters to readily alters to gypsum
Other characteristics often a pseudomorph
References [1][2][3]

Glauberite is a monoclinic sodium calcium sulfate mineral with the formula Na2Ca(SO4)2.

It was first described in 1808 for material from the El Castellar Mine, Villarrubia de Santiago, Toledo, Castile-La Mancha, Spain. It was named for the extracted Glauber's salts after the German alchemist Johann Rudolf Glauber (1604–1668).[1]

Glauberite often forms in continental and marine evaporite deposits, but may also form from hydrothermal deposits, as mineral sublimates deposited near fumaroles, in amygdules in basalt, and in nitrate deposits in arid climates. It occurs associated with halite, polyhalite, anhydrite, gypsum, thenardite, mirabilite, sassolite and blodite.[3]

Because of its solubility, glauberite is often dissolved away from the crystal matrix leaving a distinctly shaped hollow cast. Its mineral composition is readily altered into other minerals as pseudomorphs. Gypsum pseudomorphs are common due to increased humidity.

Glauberite, its cast impressions, and its pseudomorphed crystals are often easily recognizable due to its common crystal twinning, and crystal habit displayed by uniquely shaped flattened, often seeming rhombohedral, large individual 'floater crystals'.

References

  1. 1 2 Glauberite on Mindat
  2. ↑ Glauberite data on Webmineral
  3. 1 2 Glauberite in the Handbook of Mineralogy
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