Formula: Ca2Al3(Si2O7)(SiO4)O(OH) Orthorhombic
Description: Zoisite is formed in rocks subjected to low to medium grade metamorphism. If often results from the deterioration of plagioclase. It is commonly associated with epidote, clinozoisite, chlorite and albite. All of the reported Wisconsin occurrences of zoisite are as tiny grains in metamorphosed basalts and gabbros.
ASHLAND COUNTY: Zoisite is widespread as an alteration product of plagioclase in gabbroic rocks in sec. 20, 21, and 28 -31 T.45N. R.6W. near Mellen. (Leighton, 1954).
BAYFIELD COUNTY: Zoisite is widespread as an alteration product of plagioclase in gabbroic rocks in sec. 25, 35, and 36 T.45N. R.5W. and in sec. 1-9, 11-13 and 16-18 T.44N. R.5W. near Mellen. (Leighton, 1954).
MARATHON COUNTY: Zoisite is a minor accessory mineral in the Artus Creek Greenstone found in the Little Rib River area. It is intergrown with actinolite, albite, epidote and chlorite. One locality where this rock outcrops is in roadcuts along County W near Little Chicago. (Weis and LaBerge, 1969).
POLK COUNTY: Zoisite is found with epidote, chlorite, albite and actinolite formed by burial metamorphism of the Keweenawan basalts in the Dresser Trap Rock Quarry, sec. 5 and 6 T.33N. R.18W. (Cordua, 1989b).