Rare Boulder Opal and Diamond Necklace—"The Black Rainbow". Queensland, Australia

Rare Boulder Opal and Diamond Necklace—"The Black Rainbow". Queensland, Australia © 2002-2010 Bonhams 1793 Ltd

Designed and fabricated by James Currens. 2009 AGTA Spectrum Award Winner for 1st Place—Phenomenal Gemstone Category

Featuring a fancy cabochon natural boulder opal, weighing approximately 34.80 carats, exhibiting the most extraordinary ribbon pattern characterized by strong horizontal stripes of iridescent green and electric blue on an ironstone matrix. The exquisitely hand-fabricated platinum mount is embellished with 4.10 carats of brilliant-cut diamonds. The delicate and sinuous azur-work on the obverse is one of the signs of a true virtuoso platinum-smith at work, the technique is light and airy yet supportive of the stone. The pendant is suspended from a single line of briolette-cut diamonds in the necklace weighing approximately 15.87 carats, stamped PT 950 and signed J.W. Currens, length 18in. This is a unique opal for the collector and an heirloom for tomorrow. Estimate: $90,000 - 110,000. Unsold

Footnote: The boulder opal was the 2009 AGTA Spectrum Awards Winner, 1st place in the Phenomenal gemstone category.

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