WGNHS
Wisconsin Geological and Natural History Survey

Gedrite

Root-beer brown crystals of gedrite with pink pyrope garnet and white quartz. From near Granite Creek, Alder, Madison County, Montana. (Photo by W. Cordua.)

Formula: (Mg2)(Mg3Al2)(Al2Si6O22)(OH)2 Orthorhombic

Description:

Gedrite is a member of the amphibole group. It forms during medium to high grade regional metamorphism of ultramafic, iron-rich or clay-rich protoliths.

JACKSON COUNTY: Gedrite has been reported intergrown with cummingtonite in the iron formation of the Jackson County Iron Mine, SE Sect. 15 T.21N. R.3W. (Kimball, 1979).

OCONTO COUNTY: Gedrite occurs as tiny grains in metavolcanic rocks near Mountain. (Sims et al., 1991).