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.
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.)
Other 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 |
| Refractive Index | 1.715-1.725 |
Additional Information
Mineralogy Database: Spinel
Comparisons
Properties of Common Gemstones
Natural and Simulated Diamonds
Authority
- Jack Odgen, Jack Odgen, Jewellery of the Ancient World, Rizzoli International Publications Inc., New York City, 1982
- R.F.Symmes, T.T.Harding, Paul Taylor, R.F.Symmes, T.T.Harding, Paul Taylor, Rocks, Fossils and Gems, DK Publishing, Inc., New York City, 1997
- Encyclopedia Britannica, http://www.britannica.com Comment: "spinel" Encyclopdia Britannica [Accessed December 11, 2001].
- Website address 1, Website address 1 Comment: http://www.geo.utexas.edu/courses/347k/redesign/gem_notes/Spinel/spinel_triple.htm (fluorescence information)
- C.W.Chesterman, K.E.Lowe, C.W.Chesterman, K.E.Lowe, Audubon Society Field Guide to North American Rocks and Minerals, Alfred A. Knopf, New York, 1979
- Wikipedia, the free encyclopedia, at http://www.wikipedia.com Comment: http://en.wikipedia.org/wiki/Spinel (Accessed Sept. 17, 2005)
- G.S.Brady, G.S.Brady, Materials Handbook, McGraw-Hill Book Co., New York, 1971 Comment: p. 751
- Richard S. Lewis, Richard S. Lewis, Hawley's Condensed Chemical Dictionary, Van Nostrand Reinhold, New York, 10th ed., 1993
- Walter C. McCrone, John Gustave Delly, Walter C. McCrone, John Gustave Delly, The Particle Atlas, W. McCrone Associates, Chicago, IV, 1972
- Random House, 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