Abstract

A few workers (e.g., Bowen, 1938, p. 26-27) recognized many years ago that certain natural silicic glasses have unusual sodium and potassium contents. Robert L. Smith of the U. S. Geological Survey strongly suspected that natural glasses which have undergone secondary hydration (Ross and Smith, 1955; Friedman and Smith, 1958), although fresh appearing, may have lost or gained significant amounts of certain constituents in addition to water, and warned colleagues against basing petro-genetic interpretations on chemical analyses of rocks containing hydrated glass. Lipman (1965), using data from the literature and unpublished data from the files of the U. S. Geological Survey, showed that many rocks containing large amounts of secondarily hydrated glass contained significantly lower amounts of sodium and silica than did primarily crystallized (Lipman, 1965, p. D2) rocks from the same units. As discussed by Lipman, these changes are almost certainly the result of leaching of the glass and by ion exchange with ground water.

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