Opal from the Shewa Province, Ethiopia
Opal occurs as nodules in volcanic rocks at a new gem opal locality in the Menz Gishe district of Shewa Province, Ethiopia.
Queensland Boulder Opal
After almost 75 years of inactivity, the deposits of boulder opal in Queensland, Australia, began to attract new interest in the 1960s and 1970s.
Treated Andamooka Matrix Opal
Matrix opal from Andamooka, in South Australia, is a precious opal-included porous rock that is commonly colour enhanced (carbon impregnated) to imitate the highly prized black opal from Lightning Ridge in northern New South Wales, Australia.
Opals from Opal Butte, Oregon
Recent mining at Opal Butte in northeastern Oregon has produced a wide variety of large flawless opals.
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.
Abstracts; Summer 2009
This article, from the Summer 2009 issue of Gems & Gemmology, is a compilation of abstracts of important gemmology-related articles published outside of Gems & Gemmology.
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.
Opal from Querétaro, Mexico: fluid inclusion study
The distinctive orange-to-red “fire" opals from Querétaro have not been found in significant quantities at any other locality.
On the Origin of Digit Patterns in Gem Opal
An examination of the finger-like feature mostly found in Ethiopian opal and proposal for its formation.