The Beryls of the Rosses District, Donegal

A. Hall and J. N. Walsh
Department of Geology, King's College, Strand, London, WC2R 2LS

Summary: Chemical analyses and physical properties are given for six samples of beryl from greisenized granites, pegmatites, and beryl-quartz veins in the Rosses granite complex. The beryls studied were all very similar in composition and contain significant amounts of alkali elements and water in addition to the constituents represented by the formula Be3Al2Si6O18. Calculation of the empirical unit cell contents indicates that most of the H2O+ is present in the mineral as water molecules. The effects of these extra constituents on the physical properties are discussed, and it is suggested that the variation in refractive indices displayed by beryl is to a large extent attributable to the variable water content.

Mineralogical Magazine; September 1971 v. 38; no. 295; p. 328-334; DOI: 10.1180/minmag.1971.038.295.07
© 1971, The Mineralogical Society
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