Zeolites have been known since the mid-1750s, but prior to the early 1950s, most reported occurrences of zeolites were in fracture fillings and amygdules in igneous rocks, particularly basaltic lava flows. Indeed, most of the large attractive zeolite specimens in museum collections were obtained from lavas. In recent years, zeolites have been recognized as important rock-forming constituents in low-grade metamorphic rocks and in a variety of sedimentary rocks. Most zeolites in sedimentary rocks are finely crystalline, that is they occur as microscopic or submicroscopic crystals, and they are therefore of little appeal to mineral collectors; however, deposits of this type...

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