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Emeralds From the Fazenda Bonfim Region, Rio Grande do Norte, Brazil

2012; Gemological Institute of America; Volume: 48; Issue: 1 Linguagem: Inglês

10.5741/gems.48.1.2

2376-4473

J. C. Hanco Zwaan, Dorrit E. Jacob, Tobias Häger, Mario Cavalcanti Neto, Jan Canis,

Crystal Structures and Properties

In 2006, emeralds were discovered in the Fazenda Bonfim region of northeastern Brazil. Emerald mineralization occurs in association with small recrystallized pegmatitic bodies hosted by metamorphosed ultramafic rocks within the Santa Monica Shear Zone. Prospecting and exploration have been carried out in a few small pits and tunnels, producing emerald crystals with transparent areas that typically range between 2 and 5 mm. Polished samples typically show a saturated bluish green color with a medium-light to medium tone. The most common internal features are partially healed fissures with two-phase (liquid-gas) fluid inclusions and a variety of fine, parallel-oriented growth tubes. The emeralds contain moderate amounts of the chromophore elements Cr and Fe, and traces of V; they also show relatively high K and low Li. FTIR spectroscopic features are consistent with alkali-bearing emeralds that contain considerable CO 2 and a small amount of deuterated water. Emeralds from Fazenda Bonfim can be distinguished from those of other schist- and pegmatite-related commercial deposits.