Difference between revisions of "Spinel"

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Latest revision as of 17:16, 2 June 2022

Braclet with spinel
MFA# 2006.417
Spinel

Description

A hard, colored gemstone. Spinels are composed of magnesium aluminum oxide with color-producing traces of iron, zinc, chromium, or manganese. Bright red (Balas) and deep blue spinels were sometimes confused with rubies and sapphires. Spinels can also be violet (Almandine), pink, yellow (rubicelle), green, brown, or black. Spinels have been mined since at least 1000 BCE. Early deposits were found in the alluvial gravels of Sri Lanka, in limestones of Myanmar (Burma) and Thailand, and near Oxus in the Middle East. Currently, spinels are also mined in Russia, Italy, Sweden, Germany, Canada (Ontario), and the U.S. (New York, New Jersey, New Mexico, North Carolina, California). Spinels are also made synthetically as magnesia-alumina or magnesia-chromia. Industrially, the synthetic spinels are used in electronics and as refractory materials. Colorless synthetic spinels are sold as diamond substitutes in gemstone settings.

Spinel

Synonyms and Related Terms

spinelle; Balas rubies (red); spinel rubies (red); ruby spinel; magnesia spinel; rubicelle (yellow); almandine (violet); pleonast (blue, dark green, black); hercynite (iron aluminum oxide-black); gahnite (zinc aluminum oxide-dark blue-green); galaxite (manganese aluminum oxide-black); Spinell (Deut., Sven.); espinela (Esp., Port.); spinelle (Fr.); spinel (Ned.)

Physical and Chemical Properties

  • Isometric crystal system.
  • Fracture = conchoidal.
  • Streak = white.
  • Luster = vitreous.
  • Fluorescence = Natural spinel may fluoresce under long UV, but not short UV; synthetic spinel often shows colors in short UV light
Composition MgAl2O4
CAS 1302-67-6
Mohs Hardness 8.0
Density 3.5-4.1 g/ml
Refractive Index 1.715-1.725

Comparisons

Properties of Common Gemstones

Natural and Simulated Diamonds

Resources and Citations

  • Jack Odgen, Jewellery of the Ancient World, Rizzoli International Publications Inc., New York City, 1982
  • R.F.Symmes, T.T.Harding, Paul Taylor, Rocks, Fossils and Gems, DK Publishing, Inc., New York City, 1997
  • C.W.Chesterman, K.E.Lowe, Audubon Society Field Guide to North American Rocks and Minerals, Alfred A. Knopf, New York, 1979
  • G.S.Brady, Materials Handbook, McGraw-Hill Book Co., New York, 1971 Comment: p. 751
  • Richard S. Lewis, Hawley's Condensed Chemical Dictionary, Van Nostrand Reinhold, New York, 10th ed., 1993
  • Walter C. McCrone, John Gustave Delly, The Particle Atlas, W. McCrone Associates, Chicago, IV, 1972
  • 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