Glauberite

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Glauberite
Glauberite-172284.jpg
Glauberite crystal group from the Bertram Siding Sulfate deposit, Imperial County, California
General
CategorySulfate minerals, anhydrous sulfate subgroup
Formula
(repeating unit)
Na2Ca(SO4)2
Strunz classification7.AD.25
Crystal systemMonoclinic
Crystal classPrismatic (2/m)
(same H-M symbol)
Space groupC2/c
Unit cella = 10.129, b = 8.306
c = 8.533 [Å]; β = 112.19°; Z = 4
Identification
ColorGray or pale yellow, colorless
Crystal habitTabular prismatic crystals
CleavagePerfect on {001}, imperfect on {110}
FractureConchoidal
TenacityBrittle
Mohs scale hardness2.5 - 3
LusterVitreous to waxy, pearly on cleavages
StreakWhite
DiaphaneityTransparent to translucent
Specific gravity2.75–2.85
Optical propertiesBiaxial (-)
Refractive indexnα = 1.507 - 1.515 nβ = 1.527 - 1.535 nγ = 1.529 - 1.536
Birefringenceδ = 0.022
2V angle24° to 34°
Dispersionstrong r > v
SolubilityHCl and H2O (water) soluble
Alters toreadily alters to gypsum
Other characteristicsoften 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[edit]