Over the past 40 years, two universally accepted maxims of geology dealing with zeolite minerals have been shown to be incorrect: the first is that zeolites occur primarily as cavity fillings in basaltic igneous rocks, and the second is that these zeolites crystallized from so-called hydrothermal solutions, i.e. thermal waters from depth. We recognize today that enormous quantities of zeolites occur as low-temperature, low-pressure alteration products of pyroclastic material in sedimentary rocks, and that many of the zeolites filling vugs and cavities in basalts and traprocks are actually diagenetic in origin, having precipitated directly from ground water percolating through the...

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