Topaz
Description
An aluminum silicate mineral used as a semiprecious Gemstone. Topaz is usually yellow but may also be colorless, blue, brown, or pink. The transparent to translucent stone occurs most often in rocks of the Granite and Rhyolite type. Some sources of topaz are the Ural Mountains, Ilmen Mountains, Sri Lanka, Germany (Saxony), Norway, Sweden, Siberia, Scotland, Japan (Takayama, Tanokamiyama), Brazil (Minas Gerais), Mexico, and the U.S. (New England, Texas, Utah, Colorado, California). In the Middle Ages, all yellow stones were called topaz. In 1750, it was noted that yellow Brazilian topaz would turn red when heated and these were sold as Brazilian rubies.
Synonyms and Related Terms
hyacinth (dark orange); Brazilian ruby; Topas (Deut.); topacio (Esp.); topaze (Fr.); topaas (Ned.); topázio (Port.)
Physical and Chemical Properties
- Orthorhombic system with mostly prismatic crystals
- Perfect cleavage in one direction
- Fracture = subconchoidal and uneven
- Luster = vitreous
- Streak = colorless to white
- Yellow topaz turns a soft red when heated
- Pleochroism = weak to moderate; light red, orange to yellow, violet-bluish
- Fluorescence = may show yellowish color (SW) and cream color (LW)
- Inclusions = 2- and 3-phase inclusions; liquid inclusions in planes
| Composition | Al2SiO4(F,OH)2 |
|---|---|
| Mohs Hardness | 8 |
| Density | 3.4-3.6 g/ml |
| Refractive Index | 1.61; 1.61; 1.63 |
| Birefringence | 0.008 - 0.010 |
Comparisons
Properties of Common Gemstones
Resources and Citations
- Gem Identification Lab Manual, Gemological Institute of America, 2016.
- Mineralogy Database: Topaz
- 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
- A.Lucas, J.R.Harris, Ancient Egyptian Materials and Industries, Edward Arnold Publishers Ltd., London, 4th edition, 1962
- Encyclopedia Britannica, http://www.britannica.com Comment: "topaz" [Accessed December 4, 2001]. (color photo)(tech info)
- C.W.Chesterman, K.E.Lowe, Audubon Society Field Guide to North American Rocks and Minerals, Alfred A. Knopf, New York, 1979
- Wikipedia: Topaz (Accessed Sept. 17, 2005 and Dec 2022)
- G.S.Brady, Materials Handbook, McGraw-Hill Book Co., New York, 1971 Comment: p. 646
- 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
- Website: http://www.geo.utexas.edu/courses/347k/redesign/gem_notes/Topaz/topaz_three_frames.htm (fluorescence information)
- CRC Handbook of Chemistry and Physics, Robert Weast (ed.), CRC Press, Boca Raton, Florida, v. 61, 1980 Comment: density=3.5-3.6