Halite

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Halite
ImgSalt.jpg
General
Category Halide mineral
Chemical formula Sodium chloride NaCl
Identification
Color clear or white; also blue, purple, pink, yellow, and gray
Crystal habit predominantly cubes and in massive sedimentary beds, but also granular, fibrous and compact
Crystal system isometric 4/m bar 3 2/m
Cleavage perfect in three directions
Mohs Scale hardness 2 - 2.5
Luster vitreous
Refractive index 1.544
Streak white
Specific gravity 2.1
Solubility in water
Other Characteristics salty flavor

Halite is the mineral form of sodium chloride, NaCl, commonly known as rock salt. Halite occurs as cubic crystals that are typically colorless to white, but may also be light blue, dark blue, or pink. It commonly occurs with other evaporite deposit minerals such as several of the sulfates, halides, and borates.

Contents

Occurrence

Halite crystal from Germany
Halite (middle) and other salt minerals

Halite occurs in vast beds of sedimentary evaporite minerals that result from the drying up of enclosed lakes, playas, and seas. Salt beds may be up to 350 meters (1150 feet) thick and underlie broad areas. In the United States and Canada extensive underground beds extend from the Appalachian basin of western New York through parts of Ontario and under much of the Michigan basin. Other deposits in the region are in Ohio, Kansas, New Mexico, Nova Scotia, and Saskatchewan.

Salt domes and glaciers

Salt domes are vertical diapirs or pipe-like masses of salt that have been essentially "squeezed up" from underlying salt beds by mobilization due to the weight of overlying rock. Salt domes typically comprise anhydrite (anhydrous calcium sulfate, CaSO4), gypsum (CaSO4ยท2H2O), and native sulfur, in addition to halite and sylvite (potassium chloride (KCl)). They are common along the Gulf coasts of Texas and Louisiana and are often associated with petroleum deposits. Germany, Spain, the Netherlands, Romania, and Iran also have salt domes. Salt glaciers exist in arid Iran, where the salt has broken through the surface at high elevation and flows downhill. In all these cases, halite is said to be behaving in the manner of a rheid.

Large natural crystal of Halite, showing cubic cleavage breaks.

Unusual formations

Unusual, purple, fibrous veins running through halite crystals are found in France and a few other localities. Halite crystals termed hopper crystals appear to be "skeletons" of the typical cubes, with the edges present and stairstep depressions on, or rather in, each crystal face. In a rapidly crystallizing environment the edges of the cubes simply grow faster than the centers. Halite crystals form very quickly in some rapidly evaporating lakes resulting in modern artefacts with a coating or encrustation of halite crystals. Halite flowers are rare stalactites of curling fibers of halite that are found in certain arid caves of Australia's Nullarbor Plain. Halite stalactites and encrustations are also reported in the Quincy native copper mine of Hancock, Michigan.

See also

References

  • Farndon, John. The Practical Encyclopedia of Rocks & Minerals: How to Find, Identify, Collect and Maintain the World's best Specimens, with over 1000 Photographs and Artworks. London: Lorenz Books, 2006. ISBN 0754815412
  • Klein, Cornelis, and Barbara Dutrow. Manual of Mineral Science. 23rd ed. New York: John Wiley, 2007. ISBN 978-0471721574
  • Kurlansky, Mark. Salt: A World History. New York: Penguin, 2003. ISBN 0142001619
  • Pellant, Chris. Rocks and Minerals. Smithsonian Handbooks. New York: Dorling Kindersley, 2002. ISBN 0789491060
  • Shaffer, Paul R., Herbert S. Zim, and Raymond Perlman. Rocks, Gems and Minerals. Rev. ed. New York: St. Martin's Press, 2001. ISBN 1582381321
  • Mineral Gallery. The Mineral Halite. Amethyst Galleries, 2006. Retrieved September 10, 2007.
  • Spiroff, Kiril. An Unusual Occurrence of Halite. American Mineralogist. 22:931-33, 1937. Retrieved September 10, 2007.

External links

All links retrieved January 27, 2014.

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