Feature Gems & Gemology, Summer 2009, Volume 45, No. 2

Gem-Quality Andalusite from Brazil

Widely known as a rock-forming mineral, andalusite is not frequently encountered as a gem material. This article documents the gemological and spectroscopic properties of numerous rough and cut samples of gem-quality andalusite from Brazil. The color varied from yellowish green and green to brownish pink (including bicolored green and brownish pink), and some were faceted with the pleochroic colors attractively oriented. Transparent samples of the chiastolite variety of andalusite were particularly interesting. All the samples displayed a complex growth pattern, with the various inclusions oriented along the growth directions. Heat treatment produced subtle changes in color, if any, but fracture filling with resin resulted in obvious improvements in apparent clarity.