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Article: Materials handbook.(Topaz-ZTA)(Buyers Guide)
- Article from:
- Ceramic Industry
- Article date:
- January 1, 2005
CopyrightCOPYRIGHT 2005 BNP Media. This material is published under license from the publisher through the Gale Group, Farmington Hills, Michigan. All inquiries regarding rights should be directed to the Gale Group. (Hide copyright information)
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TOPAZ. [Al.sub.2][(FOH).sub.3] Si[O.sub.4.] Mohs hardness 8; sp, or. 3.4-3.6. Mined in Chesterfield County, S.C., and San Diego County, Calif.; and deposits have been reported in Brazil and South Africa. The fluorine and hydroxyl are isomorphous in the topaz structure, thus the F: OH ratio may vary considerably in various varieties. An analysis (in %) of the South Carolina topaz: 53.2 silica, 37.2 alumina, 0.4 ferric oxide, 14.1 fluorine. 0.9 LOI. Less an 0 + F of 5.9% gives 105.8%.
When calcined, the topaz crystal begins to show change at 1500[degrees]C, inversion to mullite and siliceous glassy phase begins at 2000[degrees]F and is complete at 2300[degrees]F. ...