Fourier transform infrared spectroscopic estimation of crystallinity in SiO2 based rocks.

We present here optical properties and crystallinity index of quartz (SiO₂) in natural rocks samples from the Mikir and Khasi hills, Assam, India. Infrared spectroscopy has been used to study the structure of quartz in rock samples and estimate the mining quality of quartz mineral, which is substantiated by calculating the crystallinity index. Systematic investigations of structure have been carried out in between 10 μm (1000 cm^-1) and 20 μm (500 cm^-1) bands of silicates. Investigation is based on the assignment of infrared bands to certain structural groups of SiO₄ tetrahedra. The crystallinity of samples has been ascertained by comparing the ratio of intensity of the characteristic peak at 778 and 695 cm^-1 with the corresponding ratio for a standard sample. The crystallinity parameter is calculated by using a standard procedure which can be used to estimate the distribution of quartz in various rocks for mining purpose. The infrared spectroscopic investigation is found to be an ideal tool for structure elucidation and for estimating quartz crystallinity of the natural samples. [ABSTRACT FROM AUTHOR]