Letter | Published:

Authigenic High Sanidine from Western Australia

Naturevolume 214page262 (1967) | Download Citation



AUTHIGENIC minerals grow in sedimentary rocks near the surface of the Earth or at moderate depths in the crust, supposedly at temperatures rarely exceeding 100° C. An authigenic origin has been postulated for many potassium feldspars described as microcline, orthoclase and adularia1, though in igneous and metamorphic rocks they normally form at temperatures above 100° C. Sanidine characteristically grows at temperatures far higher than the other potassium feldspars, and is restricted, with some exceptions2, to volcanic rocks. Its authigenesis is unusual and deserves discussion. The outgrowths described here are composite and contain high sanidine [2Va = 0°–60°, optic plane //(010)], low sanidine [2Va = 0°–25°, optic plane (010)], and orthoclase [2Va = 25°–70°, optic plane (010)]. There is commonly a slight departure from monoclinic optics in these minerals, with either Y or Z deviating a few degrees from the normal to (010). Low sanidine has been recorded before3, but as far as we are aware, this letter is the first report of authigenic outgrowths composed partly of high sanidine.

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    Present address: West Australian Petroleum, 251 Adelaide Terrace, Perth, Western Australia


  1. Department of Geology, University of Western Australia, Nedlands, Western Australia

    • J. E. GLOVER
    •  & P. HOSEMANN


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