Characteristics of corundums from Phuoc Hiep occurrence (Quang Nam Province)

Phuoc Hiep corundum occurrence has been discovered recently in the Central part of Vietnam (Quang Nam Province). Common protoliths in the region are high-grade metamorphic rocks (typically of amphibolite-granulite facies), such as garnet-bearing amphibolites, gneisses and schists, intruded by igneous formations of different composition and age. To date, the rubies and fancy sapphires have been found in secondary, mostly alluvial deposits. The corundum crystals occur as broken, from moderate- to well-rounded, fragments, but remains of the original habits are often present. Their size ranges from 3×5 mm to 20×30 mm, sometimes to 100×120 mm. Most of corundum pieces are of purplish pink to purplish red, with a small proportion of light to dark blue. For the first time, the gemological characteristics of Phuoc Hiep corundums are described in detail in this paper. Common gemological properties of Phuoc Hiep corundums are normal for rubies and sapphires elsewhere in the world. The most notable features are lamellar and polysynthetic (deformation) twinning, low transparency (do to high fracturing along twinning planes), color zoning and secondary, fluid, ʺfingerprintʺ inclusions. Based on the similarity in tectonic settings, geological environments, gemological and geochemical characteristics of corundums, Phuoc Hiep occurrence can be grouped into the metapelite-hosted type of corundum deposits in Vietnam, which include Tan Huong and Truc Lau deposits in the North Vietnam.