Formula: (Na,K)AlSi3O8 Triclinic
Anorthoclase is a high-temperature solid solution series found in certain volcanic and plutonic rocks.
MARATHON COUNTY: Coarse microperthitic anorthoclase showing a schiller “moonstone” occurs in a quarry in pyroxene syenite in the Stettin pluton just north of Stettin Road in the SE sec. 14 T.29N. R.6E. Xls. up to 35 cm. long occur in this pluton. At last report, the quarry is water-filled, hazardous and posted “No Trespassing”. It should be avoided unless permission is granted by the owner (LaBerge and Myers, 1983; Myers et al., 1984; Falster et al., 2000).