Extraordinary Boulder Opal Cabochon. Koroit, Queensland, Australia © 2002-2010 Bonhams 1793 Ltd 

Weighing approximately 188.0 carats and measuring 70.0 x 32.0 x 12.5mm - Sold for $8,540

This is an exceptional and very large, gem-quality pear-shaped cabochon of boulder opal exhibiting a web pattern of fine lines of electric green and blue opal in the ironstone matrix. The green and blue coloration as well as the near-metallic luster of the piece are evidence of its high iron content.

Bonhams & Butterfields. The Nature of Opals, 10 Nov 2010. 220 San Bruno Avenue, San Francisco www.bonhams.com