A Treatment Study Of Brazilian Garnets

(via The Journal of Gemmology, Vol 29, No.4, October 2004) Sigrid G Eeckhout, Antonio C S Sabioni and Ana Claudia M Ferreira writes:

Over the past decade, there has been noticeable growth in interest in colored stones worldwide, which has led to an increase in gem exploration, production and marketing. Since garnet displays a very large variety of colors, it deserves further attention. Although reports on enhanced gemstones are widespread in the gemological literature, very few studies have been performed on the enhancements of garnets. We report the first systematic, scientific treatment study on Brazilian garnets from known geological localities, including thermal and diffusion treatment. Iron-containing species become opaque and producer ‘silvery skin’. Light yellow grossular turns to orange similar to that of imperial topaz. Other garnet varieties have stable colors, confirming the absence of color centers. A preliminary diffusion treatment of some rough grossular has produced attractive green and orange stones. Since orange gemstones are becoming increasingly popular and since the diffusion treated green grossulars resemble some emeralds in color, they may be of economic importance in the future if quantities are confirmed to justify commercial mining.