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Mineralpedia Details for Andalusite

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Andalusite

Andalusite

Named for the Andalusia region of Spain, where a few localities for Andalusite lie, however none of these localities is the type locality for the mineral which actually lies in the Castile-La Mancha region of Spain.  A common and widespread mineral, additional localities can be found in Austria, Germany, the United States including here in the Black Hills of South Dakota at several mines, Australia, Sri Lanka, and Brazil, among several others. Andalusite forms as “a result of contact metamorphism of argillaceous sediments, [and] also in regionally metamorphosed schists. [It is] rare in granites and granite pegmatites, which, however, afford the largest crystals.” It can also be found as a detrital mineral in some sandstone.

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

Formula
Al2OSiO4 
Crystal System
Orthorhombic 
Crystal Habit
Blocky, Prismatic, Euhedral Crystals 
Cleavage
Distinct, Indistinct, Poor 
Luster
Vitreous (Glassy) 
Color
dark green, gray, brown, red, green 
Streak
white 
Class
Orthorhombic - Dipyramidal 
Fracture
Splintery 
Hardness
6.5-7 
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Andalusite from near Hill City, Pennington Co., South Dakota, United States

Andalusite
            from near Hill City, Pennington Co., South Dakota, United States

Large 2x2cm, purplish, blocky crystal.

Click thumbnail images for larger view.

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