IR Spectroscopy of Natural and Synthetic Amethysts in the 3000―3700 cm~(-1) Region and Problem of Their Identification

摘要

In recent years, we have scrutinized relations of formation conditions with optical absorption of natural and synthetic amethyst crystals in the 3000―3700 cm~(-1) region in order to evaluate the implication of IR spec-troscopy for their identification. We recorded and analyzed IR spectra of 580 amethyst crystals grown under standard conditions. In addition, 52 samples of natural amethyst crystals taken from deposits in Brazil, Uruguay, Bolivia, Russia, Bulgaria, and several countries of Africa were studied for comparison. The IR spectra were recorded on an Avatar 320 FT IR (Nicolet) device at room temperature in nonpolarized light. Plates (usually 2―3 mm thick) parallel to faces {c}, {x}, or other less common orientations were used. We investigated the dependence of the appearance and behavior of absorption bands on the solution composition, temperature, pressure, crystallographic orientation, growth rate, ionizing radiation (dose up to 7 Mrad, source ~(60)Co), and annealing rate at 300―700℃.