Kalsilite, a polymorph of KAlSiO4, from Uganda

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Abstract
Professor Arthur Holmes has described in the preceding paper a suite of rocks from Mafuru, Uganda. During his study he observed in thin section a mineral which in optical properties is indistinguishable from nepheline. He gives chemical evidence, however, for the presumption that a potassium aluminosilicate is present in mafurite which would suggest either that the nepheline-like mineral is kaliophilite or a polymorphous form of KAlSiO4. Kaliophilite is not isomorphous with nepheline, but has similar optical properties, and the two minerals could be easily confused in thin section. They may, however, be rapidly distinguished by X-ray methods. Even minute grains insufficient for chemical analysis can be determined with certainty; so it seemed probable that an X-ray study of the nepheline-like mineral from Uganda would give additional information and decide whether or no a separation and chemical analysis of the mineral should be attempted. Professor Holmes accordingly invited me to examine his specimens and rock-sections.
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