Feature Gems & Gemology, Winter 1988, Vol. 24, No. 4

Opals from Opal Butte, Oregon

Recent mining at Opal Butte in northeastern Oregon has produced a wide variety of large flawless opals. The most common gem-quality varieties are hyalite and rainbow opal, but the less common play-of-color varieties contra luz, hydrophane, and crystal opal are economically more important. Fire, blue, and dendritic opal are also found. The opal occurs in rhyolite geodes embedded in decomposed perlite. More than 100 kg of material was uncovered from November 1987 through November 1988. The opal varies greatly in stability, but the finest stable material makes excellent carvings, cabochons, and even faceted stones.