New Mexico Mineral Symposium — Abstracts

Peridot occurs in explosion debris from a 180,000-year-old volcano as small, but brilliant gems in a wide color range. Unlike peridot found elsewhere in the Southwest, peridot in the Kilbourne Hole maar is found in elliptical "xenolith bombs" of volcanic origin ranging from 2 to approximately 40 cm long. In chemistry, color, density and hardness, optical properties and PIXE (Proton Induced X-ray Emission) analysis, the Kilbourne peridot is similar to the San Carlos, Arizona material except for the greater color range in Kilbourne material and a characteris¬tic inclusion not heretofore described in gemological literature. The R.I.-S.G. color relationship is reviewed with regard to Mg:Fe ratio and the effect of heat treatment and irradiation. The future of this material as a source of the seldom-seen greenish-yellow "chrysolite" peridot is discussed. Comparisons made with other documented worldwide sources add to the cumulative know¬ledge we have concerning peridot as a gem material.