WGNHS
Wisconsin Geological and Natural History Survey

Foitite

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Small grains of blue foitite in quartz, as seen in thin section (a polished slice of rock about 0.03 mm thick). Yellow scale bar is 50 µm long. (Photo from Medaris and Fournelle, 2003.)

Formula: (Fe2+2Al)Al6(Si6O18)(BO3)3(OH)3(OH) Hexagonal

Description:Foitite is a member of the tourmaline group that is lacking in alkalis such as sodium.

SAUK COUNTY: Foitite and “oxy-foitite” were identified as tiny grains in quartz veins cutting the Proterozoic Baraboo Quartzite in both Baxter Hollow and Pine Hollow (Medaris and Fournelle, 2003). Associated minerals are hematite, rutile, and muscovite.