Formula: Ca2(Fe2+,Mg)Al2(SiO4)(Si2O7)(OH)2.H2O Monoclinic
Description: Pumpellyite is used to denote a group of closely related minerals that form during relatively low grade burial metamorphism. It is often associated with prehnite, epidote and chlorite. It is most common in metamorphosed basalts. Most Wisconsin pumpellyite is likely Pumpellyite-(Mg).
BAYFIELD COUNTY: Pumpellyite is found in the NW SW sec. 16 T.43N. R.9W. just west of Hwy. 27 as tiny laths and radiating xls. in amygdules and groundmass in Keweenawan basalts (Ali, 1982). Ali also refers to pumpellyite as a “subordinate” component of Keweenawan basalts throughout the Grandview-Minong area.
— Pumpellyite occurs as blue-green radiating fibers partly filling amygdules with epidote, quartz (variety agate) K feldspar, calcite, chlorite and bornite in Keweenawan volcanic rocks south of Grandview in the NW SE sec. 5 T.44N. R.6W. (W. S. Cordua field notes).
DOUGLAS COUNTY: Pumpellyite occurs are radiating fibrous masses with prehnite, epidote, chlorite and copper in amygduloidal metabasalt at the Weyerhauser Mine, NW SE Sec. 12 T. 43N. R. 10W. (W. S. Cordua field notes).