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Formula:   CaSO4   mineral photo

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Crystal:   Orthorhombic  
Hardness:   3-3.5  
Spec. Gr.:   2.98-3.0  
Streak:   White  
Cleavage:   Three at right angles  
Location:   Simplon Tunnel,

Anhydrite is formed by dehydration from the common mineral gypsum. Most anhydrite is massive in colors of blue, pink, and white, at places like: Wallaroo, South Australia; Paterson, Passaic County, New Jersey; Brumado, Bahia, Brazil; and Naica, Chihuahua, Mexico. The finest crystals were discovered when the Simplon Tunnel was being built, under the Alps between Switzerland and Italy in 1920. There, approximately 9400 meters in from the north portal, extraordinary pink columnar crystals of anhydrite were found in pockets that also contained crystals of quartz, adularia, and calcite. Gem anhydrite has a hardness of only 3-4 and therefore is difficult to cut and too soft to wear. However, it is highly prized by mineral collectors.

Bibliography: Weibel, Max, Die Mineralien der Schweiz, 1966, pg. 49.

University of California, Santa Barbara—Department of Earth Science
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