Plagioclase

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Plagioclase (feldspar)

Description

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.);

Other Properties

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

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

Additional Information

Mineralogy Database: Plagioclase

Comparisons

Properties of Common Gemstones


Sources Checked for Data in Record

  • Robert Fournier, Illustrated Dictionary of Practical Pottery, Chilton Book Company, Radnor, PA, 1992
  • Encyclopedia Britannica, http://www.britannica.com Comment: To cite this page: MLA style: "plagioclase." Encyclopædia Britannica. 2004. Encyclopædia Britannica Premium Service. 9 Dec. 2004 .
  • 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