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Formula:   Pb5(AsO4PO4)3Cl   mineral photo

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Crystal:   Hexagonal  
Hardness:   3.5-4  
Spec. Gr.:   7.24  
Streak:   White  
Cleavage:   x(101'1) Imperfect  
Location:   Tsumeb,

The best crystals of mimetite from Tsumeb were found in 1972 deep in the mine. These are gemmy, translucent to transparent, and are a pale yellow. Individual crystals, frequently in clusters, can reach a length of five centimeters, although most crystals in the large pocket were less than two centimeters. The specimen in the UCSB Geology Collection was found at about that time. Tsumeb mimetites are found in a wide range of colors and habits. Crystal forms include minute needles and crusts to small rosettes and large prismatic crystals with pinacoid and/or pyramid terminations. The color ranges from nearly colorless to pale yellow, pale brown, lemon yellow, orange, red, green, gray and black. Mimetite crystals are also found at Santa Eulalia, Chihuahua, Mexico; Roughton Gill, Cumbria, England; and at Les Farges, Corréze, France.

Bibliography: Mineralogical Record, Tsumeb Issue, V8, No. 3, pg. 28, 49-50.

University of California, Santa Barbara—Department of Earth Science
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