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T h e heat-induced alteration of iron-based impurities in gem materials is well documented in the literature. Such changes are often the goal of the gemstone enhancer, as in the heat treatment of colorless a'$ light yellow sapphire to develop or intensify 'a 'yellow color (Abraham, 1982; Keller, 1982), the heating of light yellow to brown chalcedony'to produce deep brown to red sard and carnelian colors (Nassau, 1984L and the heating of brownish yellow tiger's-eye quartz to produce a red stone (Webster, 1983). Thermal exposure may also affect iron-based inclusions, a fact that is often used to detect treatment in a stone. For example, the conversion of goethite to hematite, together with associated dehydration fracturing, has been used as evidence of amethyst-to-citrine heat treatment (Koivula, 1987a). During 1986, faceted Brazilian topazes containing brownish yellow acicular inclusions began to appear on the market. Because of the material's resemblance to rutilated quartz, dealers were describing these stones as "rutilated" topaz. Subsequent investigation by one of the authors revealed the "rutile" inclusions to be thin, etched dislocation channels colored by what appeared to be epigenetically derived (i.e., incorporated into the stone after formation) limonitic compounds (Koivula, 1987b). In the fall of 1988, one of theauthors (RCK) was shown some interesting faceted Brazilian topazes at a Santa Monica gem and mineral show. These stones had eye-visible inclusions similar to those Figure 1. This 11.77-ct colorless topaz was reportedly heat treated to alter the inclusions. Photo by William Videto.

Thermal Alteration of Inclusions in "Rutilated" Topaz