Infrared Spectroscopic Characteristics and Ionic Occupations in Crystalline Tunneling System of Yellow Beryl

Abstract

Infrared spectroscopic characteristics and ionic occupations in a crystalline tunneling system of yellow beryl crystals from Inner Mongolia, China, were investigated by standard gemological methods, laser ablation inductively coupled plasma mass spectrometry, x-ray diffraction, ultraviolet–visible (UV–Vis) spectrophotometry, and infrared (IR) spectroscopy in this study. The refractive index, specific gravity, and chemical composition of the samples are shown within the range of natural yellow beryls previously reported. The unit cell dimensions of the beryls are 9.208–9.212 A for a and 9.105–9.206 A for c with a ratio of c/a = 0.9985–0.9994. The beryl samples are generally alkali-poor beryls with Fe <0.05 and alkali <0.03 atoms per formula unit in the channel sites. The standard gemological test and mid-IR confirmed that these samples are natural beryl. However, polarized UV–Vis spectra showed an absorption band at 689 nm, and all polarized IR spectra of samples displayed a 7217-cm−1 infrared absorption in the studied samples which was associated with irradiation of the coloration. This treatment of color irradiation can be detected from the beryl channels with 689-nm absorption and 7217-cm−1 infrared absorption.