A black opal and diamond ring. Photo Bonhams

centering an oval-shaped black opal within a micro pavé diamond surround and further round brilliant-cut diamond eleven-stone shoulders; opal weighing approximately: 10.00 carats; mounted in platinum; size 5 3/4. Sold for US$68,500

Note: Purchased from the Sherman family, a third generation of opal dealers in Melbourne, Australia, this fine stone, lot 203, was carefully chosen for its spectacular range of colors, and typifies characteristics of those opals found in the Lightning Ridge. Today, Australia provides 95% of the world's supply of precious opals. Precious opals of this quality represent only .25% of the opals mined.

Opals are an amorphous mineraloid comprised of tiny hydrated silica spheres. The play of color results from the interference and diffraction of the light passing through the tightly packed spheres. Because the spheres are not uniform in size, as a precious opal is rotated we see a dynamic and colorful rainbow or opalescence.

Throughout history, the vibrant shifting colors unique to each precious opal have captivated collectors. The present stone is an exquisite gem that exhibits strong rolling flashes of reds and oranges against a blackish field. Patches of electric violet and streaks of green and yellow add depth and dimension as they appear and dissolve in a play of colors seen only in the rarest opals.

Bonhams. Fine Jewelry, 13 Dec 2011. New York, California, Los Angeles and California, San Francisco www.bonhams.com