By Russell Shor

Two of GIA's top researchers, Dr. James E. Shigley and Shane F. McClure, presented the latest findings on new synthetic and treated diamonds and characteristics of gemstones from newly discovered sources during the recent Tucson gem shows.

Addressing a seminar at the American Gem Trade Association Show Feb. 5, Shigley, who holds a doctorate in geology and is director of GIA Research, reviewed features of high pressure/high temperature (HPHT)-grown synthetic diamonds from Chatham and Gemesis, and discussed a new group of experimental chemical vapor deposition (CVD)-grown crystals from the National Center for Scientific Research at the University of Paris.

He also described how some natural diamonds are being treated by a multi-step process to produce a pink-purple, red or orangy brown color that involves HPHT annealing followed by irradiation, then lower-temperature annealing at low pressures. They show distinct characteristics, such as color zoning and fluorescence patterns, which reveal the complex treatment.

McClure, director of West Coast Identification, began the colored stone portion of the seminar by reviewing the use of laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) to detect beryllium diffusion treatment in corundum. GIA is developing a database that will help analyze trace elements in corundum. The goal is to allow gemologists to recognize untreated material more easily and help researchers anticipate future treatment processes that may come into the market.

He also discussed the differences between two types of corundum: those of metamorphic origin, as are generally found in Mogok (Myanmar), Kashmir and Sri Lanka; and those of magmatic origin, as is the typical geologic occurrence for rubies and sapphires mined in Australia, China and Thailand. Because magmatic corundum is subjected to much higher temperatures during its formation process, it often contains different mineral inclusions, and detecting whether or not it has undergone heat treatment is more difficult.

Turning to emeralds, McClure demonstrated how a newly developed fluorescence imaging instrument can help gemologists detect fracture filling.

McClure also discussed a number of new gem finds, including painite from Myanmar, scapolite from Afghanistan and orthoclase feldspar from Vietnam.