Gem News International Gems & Gemology, Summer 2016, Vol. 52, No. 2

Australian Opal Beads with Blue Play-of-Color

Opal beads with blue play-of-color.
At Tucson’s Globe-X show, these polished Australian opal beads (in sandstone matrix) displayed blue play-of-color. Photo by Donna Beaton.

The Australian Opal Shop (Gold Coast, Australia) had a variety of goods on display at Tucson’s Globe-X Gem & Mineral Show. Owner John McDonald primarily deals in boulder opal with a sandstone matrix from the Winton mining area in Queensland. Untreated specimens can be polished to create beautiful slabs of boulder opal with or without matrix, though sandstone with microscopic bits of opal must be treated to make the play-of-color visible. The pieces are soaked in a fatty oil (usually vegetable oil) rather than petroleum-based oils, which leave a residue. The finished product ranges from multicolored to dark blue, depending on the size of the opal pockets and the spherical structure. What appears as dark blue bodycolor is actually blue play-of-color. The treated rough is usually fashioned into beads.

Donna Beaton is colored stones technical advisor for content strategy at GIA.