Cochise College          Photos of Minerals

                          Geology Home Page                

                          Roger Weller, geology instructor

                                  copyright 2006-R.Weller

Mineral Information on:

Chemical Group:    silicate  (plagioclase feldspar)

Chemical Formula:   
  CaAl2Si2OAnorthite 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


Occurrences:  Franklin, New Jersey

Toxicity:      when-swallowed- moderate              when inhaled- high

Additional Information: