From Gems & Gemology: Winter Issue Features Dyed Ethiopian Opal, Diamond Symmetry Grading

CARLSBAD, Calif. – Jan. 25, 2012 – The Winter 2011 issue of GIA’s (Gemological Institute of America) Gems & Gemology (G&G) examines a new dyed purple opal, GIA’s diamond symmetry grading boundaries, and more.

In the lead article, GIA researchers Nathan Renfro and Shane McClure investigate an opal with an unusual purple bodycolor and strong play-of-color. Although the material was initially represented as originating from a new deposit in Mexico, evidence indicates it is actually dyed opal from Ethiopia’s Wollo Province. The porous nature of this hydrophane opal makes it susceptible to many kinds of treatment, which could pose a host of new identification challenges.

Next is Dr. Don Hoover’s method for deriving garnet composition from magnetic susceptibility and other measurable properties. Many of the garnet compositions derived from this method correspond closely with results obtained from chemical data.

In the third feature article, GIA researchers present the symmetry grading boundaries for round brilliant cut diamonds. In early 2012, these values will be used to support and constrain visual symmetry grading on GIA diamond reports.

Other articles explore a 19th-century jewelry set that contains fossilized dentine (odontolite) as a turquoise imitation, plus the radioactive decay pattern of London Blue neutron-irradiated topaz, which may require several years to “cool off” before it is safe to handle.

The Lab Notes section features a rare Fancy Vivid purple diamond, a black opal from Ethiopia, a strand of large coated bead-cultured freshwater pearls, and much more. In the Gem News International section, contributors from around the globe report on sugar-acid treatment of Ethiopian opal, color-change sphene from the Pakistan/Afghanistan border, and intensely blue spinel from Vietnam, to name a few.

The issue also includes a ballot for this year’s Most Valuable Article Award. Vote for the top three G&G articles of 2011 and enter to win a free one-year subscription, plus a flash drive containing every issue from the past 10 years.

To subscribe to G&G, visit the GIA Store, contact circulation coordinator Martha Rivera at martha.rivera@gia.edu or call toll-free (800) 421-7250, ext. 7142. From outside the U.S. and Canada, call (760) 603-4000, ext. 7142. To purchase PDF versions of articles or sections, visit Gems & Gemology Online.