The Microscopical Examination and Identification of Crystalline Products in Commercial Glasses

JSGT_1937_V21_T395_T408

Frequently it is possible to examine and identify crystalline inclusions in glasses without the necessity for preparing microscope sections. All the commonly occurring crystalline products so found possess the property of straight extinction, and the use of doubly polarised light is of value, chiefly in the recognition of the different crystal species, by their characteristic appearance when viewed between crossed Nicols. Photographs are given showing the crystalline forms and habits of quartz, cristobalite, tridymite, wollastonite, pseudo-wollasstonite, barium disilicate, kyanite, sillimanite, mullite, and corundum, when found in commercial glasses. The deposition of sodium sulphate in sulphate boils and scabs is illustrated, and also the use of powder methods, the Becke line test, and chemical analysis with reference to the identification of devitrite, sodium disilicate, and a magnesium aluminium silicate, respectively.

 A. J. Holland & Eric Preston