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Mineralpedia Details for Anhydrite

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Anhydrite

Anhydrite

Named from the Greek anydos, which means “waterless”, or “dry,” in reference to the lack of water in the composition as opposed to the very similar Gypsum, which contains water in its composition. Anhydrite is a common mineral that can be found in evaporate deposits, in cap rocks above salt domes, as a dehydration product of gypsum, in igneous rocks, fumarolic deposits, surrounding hydrothermal chimneys, and as an alteration product in hydrothermal mineral deposits. Associated minerals include gypsum, halite, sylvite, polyhalite, dolomite, calcite, magnesite, celestine, and sulfur. Anhydrite can be rehydrated to gypsum. Colorless to pale blue-violet, white, pink, brown, or gray tabular crystals that can occur in granular, nodular, divergent, fibrous masses. Anhydrite can have a pearly to vitreous to greasy luster.

Ref. Handbook of Mineralogy, Anthony et al (1995) and MSA at http://www.handbookofmineralogy.org/pdfs/anhydrite.pdf

Formula
CaSO4 
Crystal System
Orthorhombic 
Crystal Habit
Massive - Granular, Massive - Fibrous, Plumose 
Cleavage
Perfect, Perfect, Good 
Luster
Vitreous - Pearly 
Color
colorless, white, bluish white, violet white, dark gray 
Streak
white 
Class
Orthorhombic - Dipyramidal 
Fracture
Brittle - Conchoidal 
Hardness
3.5 
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Anhydrite from Homestake mine, Lawrence Co., South Dakota, United States

Anhydrite
            from Homestake mine, Lawrence Co., South Dakota, United States

Colorless bladed to tabular anhydrite crystals from 8mm to 1 cm.

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Anhydrite from Chihuahua, Mexico

Anhydrite
            from Chihuahua, Mexico

Light blue long bladed Anhydrite crystal group.

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Anhydrite from Strathcona mine, Sudbury, Ontario, Canada

Anhydrite
            from Strathcona mine, Sudbury, Ontario, Canada

Purple cleavages of Anydrite on matrix with some sulfides.

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Anhydrite from Champion mine, Marquette Co., Michigan, United States

Anhydrite
            from Champion mine, Marquette Co., Michigan, United States

A good geological specimen from this important mine. It features crystalline light purple anhydrite throughout with Hematite(?).

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