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Named for an island in the Red Sea that was referred to as Topazios or Topazion, and is called St. John’s Island today. The name of the island itself refers to its difficulty to be found, as Topazion means “to seek” in Greek. The island was not known for the mineral Topaz, however, and any reference to Topaz in ancient texts actually translates to the yellow green olivine variety peridot. Topaz can befound in veins and cavities within granites, pregmatites, rhyolites and is formed from hot, volatile, hydrothermal fluids. It can also be found in high-grade metamorphic and as a detrital mineral. It can be found in thousands of localities worldwide. Topaz can, albeit rarely, fluoresce under ultraviolet light. Topaz from certain localities must be kept away from sunlight, such as the brown variety from Baldface Mountain, New Hampshire, USA and the sherry-colored crystals from The Cove, Utah, USA, as the color may fade with exposure.
Ref. Handbook of Mineralogy, Anthony et al (1995) and MSA at http://www.handbookofmineralogy.org/pdfs/topaz.pdf