Jump to navigation Jump to search



A mineral composed of hydrated Calcium borate. Colemanite occurs in massive deposits and monoclinic crystals. Named after William T. Coleman, the mineral was originally found in 1884 in Death Valley, California. It is currently mined in Turkey. Colemanite can be colorless, milky or gray and transparent to translucent. It is a principal source of Borax and Boric acid. Colemanite is used in the manufacture of Glass, glass fibers, and ceramic glazes.



Synonyms and Related Terms

hydrated calcium borate; Gerstley borate; colémanite (Fr.); colémanita (Esp.); Colemanit (Deut.)


  • Contact and ingestion will burn skin and tissues

Physical and Chemical Properties

  • Monoclinic system with prismatic crystals or massive or granular.
  • Perfect cleavage in one direction; good in a second direction.
  • Luster = vitreous to adamantine.
  • Fracture = subconchoidal.
  • Streak = white.
Composition Ca2B6O11-5H2O
Mohs Hardness 4.0 - 4.5
Density 2.26-2.48 g/ml
Refractive Index 1.445;1.469;1.472

Resources and Citations

  • Michael McCann, Artist Beware, Watson-Guptill Publications, New York City, 1979
  • 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
  • Richard S. Lewis, Hawley's Condensed Chemical Dictionary, Van Nostrand Reinhold, New York, 10th ed., 1993
  • Van Nostrand's Scientific Encyclopedia, Douglas M. Considine (ed.), Van Nostrand Reinhold, New York, 1976
  • 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