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Plagioclase (feldspar)


A common series of feldspars that contain both calcium and sodium aluminum silicates. Placiogclase minerals fall in between the categories of Albite (sodium aluminum silicate) and Anorthite (calcium aluminum silicate). Examples of plagioclase minerals are: Labradorite, and sunstones. Some rocks that contain plagioclase minerals are: andesite, Basalt, Diabase, Diorite, and Gabbro.

Synonyms and Related Terms

soda lime feldspar; oligoclase; labradorite; bytownite; plagioclase (Port.);

Physical and Chemical Properties

Good cleavage in two directions. Fracture = uneven. Luster = vitreous. Streak = white

Mohs Hardness 6.0-6.5
Density 2.62-2.76 g/ml
Refractive Index 1.53-1.59


Properties of Common Gemstones

Resources and Citations

  • Robert Fournier, Illustrated Dictionary of Practical Pottery, Chilton Book Company, Radnor, PA, 1992
  • C.W.Chesterman, K.E.Lowe, Audubon Society Field Guide to North American Rocks and Minerals, Alfred A. Knopf, New York, 1979
  • Random House, Webster's Encyclopedic Unabridged Dictionary of the English Language, Grammercy Book, New York, 1997
  • The American Heritage Dictionary or Encarta, via Microsoft Bookshelf 98, Microsoft Corp., 1998

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