WGNHS
Wisconsin Geological and Natural History Survey

Glaucophane

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