Formula: Ca2Mg5Si8O22(OH)2 Monoclinic
Description: Tremolite is formed by the metamorphism of calcium-rich rocks such as limestone and dolostone. It occurs in numerous Precambrian rocks in the state, such as in Bad River dolomite (now metamorphosed to a marble) in Bayfield and Ashland Counties; in the rocks hosting massive sulfide deposits near Rhinelander and the talc mines near Milladore.
ASHLAND COUNTY: Tremolite is often found in the Bad River Dolomite such as outcrops “under the railroad bridge at Penokee Gap” along the Bad River in SE NW sec. 14 T.44N. R.3W.and in SE NW sec. 24 T.44N. R.3W. (Van Hise and Irving, 1892).
- Tremolite occurs locally in the metamorphosed Ironwood Iron Formation with grunerite, actinolite and various pyroxenes. Some localities of tremolite-bearing iron formation are in a roadcut on the west side of highway 13 about 5 km. south of Mellen (SE NW Sec. 13 T.44N. R.3W.) and in outcrop at the Mineral Lake Lookout Tower (NE NE sec. 24 T.44N. R.4W) (Laybourne, 1979).
BAYFIELD COUNTY: Pale green tremolite crystals in individuals and radiating groups up to several cm. long are common in the Bad River dolomite worked at the Grandview Marble Quarry in the NW NW NW sec. 22 T.44N. R.5W. Some layers in the marble are almost pure tremolite. Tremolite forms rims separating quartz grains and pods form the carbonate. Pyrite, chlorite, magnetite and sericite are associated minerals. (Mudrey, 1979).
- Tremolite is found in outcrops of the Bad River dolomitic marble near the Marengo river in the SW sec. 15 T.44N. R15W. The tremolite forms radiating clusters and coarse crystals in veins. (Van Hise and Irving, 1892; Leighton, 1954).
FLORENCE COUNTY: Tremolite occurs with diopside in a drill core from the Bass Lake area in T.38N. R.17E. (Nielsen, 1984).
ONEIDA COUNTY: Tremolite is found in the sequence of talc and calc-silicate-rich rocks that host the Lynne Au-Ag-Zn-Pb massive sulfide ore body in the SW corner of Oneida County. (Kennedy et. al., 1991).
- Tremolite occurs with scapolite, diopside and grossular in calcite in veins cutting the intensely altered volcanic rocks at the Pelican River massive sulfide deposit in sec. 29 T.36N. R.9E., east of Rhinelander (Bowden, 1978).
POLK COUNTY: Tremolite occurs locally at the Dresser Trap Rock Quarry (sec. 5 and 6 T.33N. R.18W.). Here it forms asbestiform fibers up to 5 cm. long on joint surfaces where they are intergrown with calcite and associated with quartz and epidote. (Cordua, 1989b).
WOOD COUNTY: Tremolite is common in schist with talc, magnetite, actinolite, pyrite and chlorite at the Something Talc Mine (old Czaikowski Property) north of Milladore. (NE SW sec. 15 T.25N. R.5E.). Asbestiform tremolite is also found at the nearby Trowbridge talc mine (SW NW sec. 11 T.25N. R.5E) where it occurs in talc and chlorite schists. (U.S. Bureau of Mines, 1963; Aldrich, 1928.)