Cochise College          Photos of Minerals

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                          Roger Weller, geology instructor

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                                  copyright 2006-R.Weller
 

Mineral Information on:
anorthite

Chemical Group:    silicate  (plagioclase feldspar)

Chemical Formula:      CaAl₂Si₂O₈  Anorthite is the calcium end member of the plagioclase feldspars. 
     Anorthite ranges from 0% to 10% NaAlSi₃O₈ and 100% to 90% CaAl₂Si₂O₈.

Color: white, gray, reddish       Transparency:  transparent to translucent                   

Streak:  uncolored        Luster:  vitreous, pearly        Tenacity:  brittle

Hardness:  6 to 6.5             Specific Gravity:  2.74 to 2.76                  

Fracture:   uneven to conchoidal

Cleavage:  (001) perfect and (010) slightly less

Crystal Forms: Triclinic system
     Crystals prismatic
     Commonly shows polysynthetic (plagioclase) twinning.

Mineral habits:  massive, granular, coarse lamellar
    
Mineral Associations:  found in andesite, basalt, gabbro, norite

Identifying Characteristics:  white color, plagioclase twinning

Uses:

Occurrences:  Franklin, New Jersey

Toxicity:      when-swallowed- moderate              when inhaled- high

Additional Information: