Beryl-muscovite pegmatites within quartzites and sillimanite schists of the middle Proterozoic Umkondo system in the Zambezi Rhodesian massif metamorphic belt. Their absolute age is 480 to 680 Ma.
Gem-quality greenish blue, pale blue, golden, yellow, and colourless beryl
was recovered from weathered zone, which considerably enhanced mining.
Transparent material free of inclusions and fractures is trimmed from larger feculent crystals. Light yellow beryl
dominates in the upper parts of the pegmatite body, greenish and blue aquamarine
are more abundant at depth. RI for yellow beryl
is 1.574-1.580, density is 2.721 g/cm³, RI for aquamarine is 1.578-1.584 and density is 2.725g/cm³.
Ref: E.Ya. Kievlenko, Geology of gems, 2003, p. 114
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