Kafubu Emerald District, Lufwanyama, Copperbelt, Zambia

Kafubu emerald-bearing field was discovered in the 1950s. The basin of the Kafubu river contains a number of emerald-bearing deposits, which are restricted to three zones in the easterly striking ultramafic schists. The quartz-tourmaline veins contain rare small emeralds of poor quality. Gem-quality emeralds are extracted only from biotite-phlogopite rock. Emeralds of the best quality are hosted in the fine-grained, massive glimmerite. Emerald accumulations tend to occur in the shallow-dipping parts of the undulating glimmerite veins.

The emerald crystals range from 1 mm to 10 cm long, sometimes with intergrowths of several parallel crystals. The crystals of very high gem-quality may weigh as much as 30 g. Faceted stones usually weigh from 0.25 to 15 ct.

The best Zambian emeralds are transparent with deep, bright-green colour, some of them have a yellowish tint. Bluish green crystals, enriched in iron, are considered as varieties transitional to aquamarine (Schmetzer and Bank, 1981). The inclusions are phlogopite, tourmaline, magnetite, apatite, minor hematite, margarite, chrysoberyl, rutile, quartz, garnet and calcite. RI is very high 1.592 - 1.602, density is 2.71 - 2.77 g/cm³.

Ref: E.Ya.Kievlenko, Geology of gems, 2003, p. 87

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