Cochise College          Photos of Minerals

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                          Roger Weller, geology instructor

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                                  copyright 2006-R.Weller
 

Mineral Information on:
oligoclase

Chemical Group:    silicate  (plagioclase feldspar)

Chemical Formula:      Oligoclase is a mid-composition plagioclase feldspar 
     Oligoclase ranges from 90% to 70% NaAlSi₃O₈ and 70% to 50% CaAl₂Si₂O₈.

Color: white, gray, reddish, greenish, yellowish, brown, colorless  
     Sometimes displays schiller, a bluish or multi-colored opalescence    

Transparency:  transparent to translucent                   

Streak:  uncolored        Luster:  vitreous, pearly        Tenacity:  brittle

Hardness:  5 to 6             Specific Gravity:  2.60 to 2.75                  

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:  diorite, gabbro, norite, andesite

Identifying Characteristics:   plagioclase twinning and schiller

Uses:  gemstone, decorator rock

Occurrences:  Norway, Sweden; new York, Pennsylvania, North Carolina

Toxicity:      when-swallowed- moderate              when inhaled- high

Additional Information: