A new booklet by New York's European Gemological Laboratories (EGL) is intended to help jewelers learn more about high-pressure, high-temperature (HPHT) treated diamonds. Gregory E. Sherman, the lab's director of marketing and education and the booklet's co-author, says the lab has been in touch with the major producers of these diamonds, both in the United States and in Russia. The booklet gives an introduction to identifying treated yellow and green stones, which scientists consider the easiest to identify. "It's such an important area that's evolving all the time, and we'd like to help jewelers learn about this," he says. EGL is giving seminars on the subject at GIA chapters throughout the country. To order the booklet, call (212) 730-7380, ext. 214.