Carnaíba mining district, Pindobaçu, Bahia, Brazil

Large deposit in the state of Bahia, SW of the town of Senhor do Bonfim was discovered in 1957. Emerald is localized in the aposerpentinite metasomatites, which developed near the granites in the magmatized rocks and directly in the granites as a large xenolith. Emerald and alexandrite occur in metasomatic biotite-phlogopite and phlogopite-talc rocks. Emerald crystals are disseminated in the glimmerites and are generally 2 to 3 cm long. The largest crystals may reach 4.5 X 12 cm in size, but they have numerous defects and don't have gem value. Emeralds contain inclusions of biotite, phlogopite, muscovite, chlorite and minor tourmaline, albite, molybdenite, goethite, lepidocrocite, tremolite, actinolite, quartz, and pyrite. Small, two- or three-phase inclusions are common. Density is 2.70 - 2.72 g/cm³. Quality of the emerald raw material, especially during the first years of deposit exploitation, was not high. Operations later concentrated on the best areas, which increased the amount of cuttable stones.

Ref: E.Ya. Kievlenko (2003) Geology of gems, p. 90

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