Amethyst

Heat treatment between 878 - 1382 degrees F (470 - 750 degrees C) produces light yellow, red-brown, green, or colorless varieties. The original color an be restored by X-ray radiation. - Gemstones of the world, Walter Schumann, 2001, p 118 Synthetic amethyst produced by hydrothermal method entered the market in 1970s. 7Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) 2.65Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004) BrittleWalter Schumann, Gemstones of the world (2001) Very brittle NoneWalter Schumann, Gemstones of the world (2001) ConchoidalWalter Schumann, Gemstones of the world (2001) The colour does not resist high temperatures. When subjected to the action of heat it changes first to a more or less pronounced yellow, gradually assumes a greenish shade, and finally disappears.Max Bauer, Precious Stones (1968) Dover Publications 1.544 to 1.553Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) 0.009Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004) Weak: (gray)-purple - reddish-purpleHerve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) 0.013Walter Schumann, Gemstones of the world (2001) Purple, violet, pale red-violetWalter Schumann, Gemstones of the world (2001) More from other references Some amethysts lose some color in daylight.Walter Schumann, Gemstones of the world (2001) ReddishHerve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) Violet to purple, O2+→Fe4+ charge transfer, due to irradiation.W. William Hanneman, Pragmatic Spectroscopy For Gemologists (2011) Transparent,TranslucentUlrich Henn and Claudio C. Milisenda, Gemmological Tables (2004) Inert to weak greenish or bluishHerve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) TrigonalUlrich Henn and Claudio C. Milisenda, Gemmological Tables (2004) Hexagonal prismsWalter Schumann, Gemstones of the world (2001) Found in geodes in alluvial deposits.Walter Schumann, Gemstones of the world (2001) Amethyst information at mindat.org Bolivia  Laurs (2001, 2010) Laurs (2001, 2010) Laurs (2001, 2010) Brazil  Couto (2000) Priester (1999) Rocks & Min.:5:131. Rocks & Min.: 5:131. Rocks & Min.:5:131. Balzer (1999) R. Batista and D. Epstein (2000) Cambodia  Ngu and Ngoc (1986) Canada  Garland (2004) Sinkankas (1997) Sinkankas (1997) India  S. Fernandes (1999) Kenya  Henn and Milisenda (2001) Madagascar  Aurisicchio et al. (1999) Madagascar, extraLapis English No.1, 2001, p. 44 Pezzotta (1999) Madagascar - extraLapis English No.1, p. 92 Mexico  Ontiveros et al. (2004) Ontiveros et al. (2004) Myanmar  Ted Themelis (2008) Gems & mines of Mogok Ted Themelis (2008) Gems & mines of Mogok Ted Themelis (2008) Gems & mines of Mogok Namibia  Michelou (2006) Nigeria  Laurs and Koivula (2003) Peru  Russia  P. Lyckberg (2009) V. Bukanov (1999) V. Bukanov (1999) South Korea  Yang et al. (2001) Sri Lanka  Uruguay  Gilg et al. (2003) mindat.org USA  Lowell and Koivula (2004) Laurs (2005)