Gem-quality augite from Dong Nai, Vietnam
Le Ngoc Nang, Lam Vinh Phat, Pham Minh Tien, Pham Trung Hieu, Kenta Kawaguchi, Pham Minh
Augite from Dong Nai Province in Vietnam occurs as xenocrysts hosted by Cenozoic basalt and its regolith. Found as irregularly shaped crystals a few millimeters to centimeters in size, these augites exhibit two dominant colors: brown and green. They are very dark in tone, making them appear almost black in reflected light and are translucent to transparent, with vitreous luster. Most of the samples’ gemological properties are similar except for refractive index and birefringence values, which are both higher in green augite. The brown and green augite samples show differences in Raman peak positions. The chemical composition as determined by electron probe microanalysis suggests that Dong Nai augite should be classified as magnesium-rich augite. This material is promising for jewelry use, as gem-quality material is readily found over a large area.