This 65.7-carat chunk of seam opal hails from the old Zorba field in Coober Pedy, South Australia. This dazzling stone boasts a spectacular array of bright yellow-green and blue hues. Our goal is to transform this impressive piece into a cabochon, but as I examine the stone, I note a finding that teaches an important opal lesson: a wedge-shaped defect on the edge nearly always indicates an underlying crack in the opal.
Wedge defects are found with similar properties to opal, like flint, chert and chalcedony. In this opal, a crack was present, but a careful approach minimized loss. T