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Green Opal From East Africa

John I. Koivula and C. W. Fryer, December 1, 1984

Gemmological and chemical analysis of bright green gem-quality opal from Tanzania.

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Opal from Queretaro, Mexico: Occurrence and Inclusions

John I. Koivula, Chuck Fryer, June 1, 1983

An examination of play-of-colour opal from Mexico and its variety of inclusions.

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Chrysoprase and Prase Opal from Haneti, Central Tanzania
Chrysoprase and Prase Opal from Haneti, Central Tanzania

James E. Shigley, Brendan M. Laurs, and Nathan D. Renfro

Commercial quantities of gem-quality chrysoprase and green prase opal (nickel-bearing chalcedony and common opal, respectively) have been recovered from altered serpentinite deposits near Haneti, Tanzania.

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