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Mineralpedia Details for Mansfieldite

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Mansfieldite

Mansfieldite

Named to honor Dr. George Rogers Mansfield, a former geologist at the United States Geological Survey. Mandfieldite is an uncommon mineral that occurs of hydrothermal origin in altered and mineralized andesitic pyroclastic rocks at its type locality at Hobbart Butte in Oregon, USA. Other localities for Mansfieldite include in Mexico, Germany, France, England, Algeria, Australia, and Kazakhstan.

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

Formula
AlAsO4ยท2H2
Crystal System
Orthorhombic 
Crystal Habit
Spherical, Encrustations 
Cleavage
Indistinct, None, None 
Luster
Vitreous (Glassy) 
Color
white, light gray, reddish gray 
Streak
white 
Class
Orthorhombic - Dipyramidal 
Hardness
3.5-4 
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Mansfieldite from Mt. Cobalt mine, Mt Isa, Queensland, Australia

Mansfieldite
            from Mt. Cobalt mine, Mt Isa, Queensland, Australia

Mansfieldite occurs as light pink, drusy crystals with probable rhombic dipyramidal micro crystals. It is very hard to actually see these crystals even under the scope. However, because of the triangular reflections of the faces, and the description of these forms in the December 1995 issue of Australian Journal of Mineralogy (V. 1, N. 2), they are most likely the same crystal form. The same description also points out that the pink color is caused by Cobalt impurities, otherwise Mansfieldite, an aluminum arsenate, is white to light blue.

Pink, translucent cobaltoan Mansfieldite crystals to about 0.8mm

Click thumbnail images for larger view.

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