Structural defects in microcrystalline silica

• Published in: Physics and chemistry of minerals Vol. 14; no. 3; pp. 249 - 257
• Main Authors: GRAETSCH, H, FLÖRKE, O. W, MIEHE, G
• Format: Journal Article
• Language: English
• Published: Berlin Springer 01-03-1987
• Subjects: Earth sciences; Earth, ocean, space; Exact sciences and technology; Mineralogy; Silicates; X-ray data; Infrared spectrometry; Infrared spectroscopy; Chemical analysis; Cell dimensions; Specific gravity; Refractive index; Refraction index; Chemical composition; Density; Silica; Polymorphism
• ISSN: 0342-1791; 1432-2021
• DOI: 10.1007/BF00307990

The structure of the microcrystalline silica varieties chalcedony, flint, moganite, opal-C and -CT is characterized by X-ray powder diffractometry and transmission electron microscopy (TEM). The role of impurities is investigated by infrared spectroscopy and chemical analysis. Microcrystalline opal, chalcedony and flint have a disordered intergrowth structure composed of cristobalite and tridymite domains in opal, and quartz and moganite domains in chalcedony and flint. Each constituent phase has different cell dimensions and symmetry. The main impurity is water which is enriched at the intergrowth interfaces. Density and refractive indices of microcrystalline silica depend on the water content. 46 ref.--AA