Green Opal From East Africa
Gemmological and chemical analysis of bright green gem-quality opal from Tanzania.
Opal from Queretaro, Mexico: Occurrence and Inclusions
An examination of play-of-colour opal from Mexico and its variety of inclusions.
Chrysoprase and Prase Opal from Haneti, Central Tanzania
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.