There are few places in the state that don’t have quartz in some form. Quartz also forms the bulk of unconsolidated sediments such as drift and alluvium, where it can be found occasionally as Lake Superior agates freed from their volcanic matrix by erosion. It forms as a groundwater precipitate, and can form sparkling crystals lining cavities in quartzite, limestone and dolostone. ![]() It is a common hydrothermal mineral and forms in amygdules in volcanic rock, sometimes in the form of Lake Superior agate. It is an essential component of granitic igneous rocks, of sedimentary rocks such as sandstone and chert and of metamorphic rocks such as quartzites. Cordua.)ĭescription: Quartz is the most abundant mineral. Large “thunder egg” with agate, drusy quartz and clay fill.įrom Iron County, Wisconsin.
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