WGNHS
Wisconsin Geological and Natural History Survey

Glaucophane

Glaucophane with pen for scale. From the mineral collection of Brigham Young University Department of Geology, Provo, Utah, courtesy of the U.S. Geological Survey Denver Library Photographic Collection. (Photo by Andrew Silver.)

Formula: Na2(Mg3Al2)Si8O22(OH)2 . Monoclinic

Description:

Glaucophane is a blue member of the amphibole group that forms in metamorphic rocks that are either particularly rich in sodium or that have experienced low temperature-high pressure metamorphism such as would occur along a subduction zone.

FLORENCE COUNTY: Glaucophane is a minor accessory mineral in grunerite-magnetite-quartz stilpnomelane rock found at several points west of Florence. Outcrops are in sec. 26, 35 and the W 1/2 sec. 36 T.40N R.17E. and in sec. 1 T.39N. R.17E. (Dutton, 1971).