Anhydrite Microscopic

KEY WORDS gypsum, microscopes, polarization, birefringence, limestone, silicon dioxide. anhydrite, refractivity. extinction angle, dispersion staining... 

The microscope is a great tool to have around a gypsum laboratory. The polarizing microscope in particular is perhaps the fastest and most accurate means for qualitative analysis of gypsum. It can also be put to work doing some quantitative analysis of anhydrite in gypsum. 

The fastest method of analyzing a specimen on the microscope is to merely look at it and make an estimate of the percentage of natural anhydrite present. 

Further if a known weight or volume of sample is counted, then it is not necessary to count the gypsum particles but only the anhydrite or other components of interest. The microscope can then be quite useful in analyses of natural anhydrite in gypsum. 

Gardner. H. F., Notes on the Chemical and Microscopic Determinations of Gypsum and Anhydrite. Proceedings 26, Vol. I, American Society for Testing and Materials. Philadelphia. 1926. pp. 296. 

In 1967, Hardie (G24) reported on this extremely slow rate of reaction. The first experimental- technique he tried involved the additions of anhydrite or gypsum to sodium sulfate solutions in tubes that were sealed and placed in a water bath for temperature maintenance. After test periods of several days to several months, the tubes were opened and the solids present were examined under the microscope and by X-ray diffraction. Although the solution volumes were too small for... 

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