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A calcium-rich plagioclase feldspar mineral composed of calcium aluminosilicate. Anorthite occurs as brittle, translucent, white ,or gray crystals. It is found in many igneous rocks such as Gabbro and Granite. Major deposits occur in Italy (Trentino, the lavas of Vesuvius, and Monte Somma), Finland, Sweden (Södermanland), India (Tamil Nadu), Japan (Miyake), and the United States (New Jersey).

Synonyms and Related Terms

calcium feldspar; Anorthit (Deut.); anorthiet (Ned.); anortyt (Pol); anortita (Esp.); anortite (Port.); anortyt (Ned.)


Anorthite PMA.TIF



Other Properties

Crystalline system = triclinic Cleavage = perfect in one direction Pleochroism = yellow to dark green to transparent to opaque

Luster = vitreous
Composition CaAl2Si2O8
Mohs Hardness 6.0-6.5
Density 2.74-2.76
Refractive Index 1.51

Sources Checked for Data in Record

  • Robert Fournier, Illustrated Dictionary of Practical Pottery, Chilton Book Company, Radnor, PA, 1992
  • The American Heritage Dictionary or Encarta, via Microsoft Bookshelf 98, Microsoft Corp., 1998
  • CRC Handbook of Chemistry and Physics, Robert Weast (ed.), CRC Press, Boca Raton, Florida, v. 61, 1980 Comment: density=2.74-2.76

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