Paper No. 1
Presentation Time: 8:05 AM


ROSSMAN, George R., Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125-2500,

Gemological laboratories are facing challenges as a result of the ever increasing sophistication of treatment methods that are used to modify the color, clarity and appearance of gem materials. In addition, the increasing demand for locality information about the origin of individual gems has put new demands on the information that must be obtained from faceted stones. There are several analytical methods that are commonly applied in the geochemical community to address a variety of research needs that, in principle, could prove highly useful for gemological problems, but which have seen sparse application in the gemological community. Tools such as electron paramagnetic resonance (EPR), oxygen isotopic studies, and argon isotopes are three methods that immediately come to mind. One of the reasons for their infrequent application rests on the need to minimize destruction to gemological samples. Tests often are conducted under the requirement of near-invisible damage to the sample. Another part of the lack of their application involves both the relative unfamiliarity of the method in the gemological communities and expense of the instruments and the attendant laboratory infrastructure.

EPR has proven to be highly important in the study of color centers in diamond, but could also have wider application to issues involving colored stones. An example of the sensitivity of EPR in a gemological setting is the detection of the O- center that accompanies the diffusion of beryllium into corundum to alter the color of the phase. Oxygen isotopes have seen limited application to the problems of the provenance of the corundum gems and emeralds, but could be widely applied to a variety of gems if less-damaging and less-costly methods of analysis could be devised. An excellent example of the adaption of advanced geochemical tools involves the recent controversy about red andesine feldspar from China. The definitive proof needed to show that these gems were colored by diffusion of copper in a laboratory setting came from the examination of argon isotope ratios that showed that radiogenic argon from the decay of 40K had been recently removed from the stone by a process involving significant heating at temperatures far in excess of the heat generated during normal cutting, faceting and polishing operations.