Formula: CaFeSi2O6 Monoclinic
Description: Hedenbergite is a dark green to black member of the pyroxene group. It usually forms due to metamorphism of iron-rich or carbonate-rich sedimentary rocks or as a primary mineral in certain syenites and related rocks.
JACKSON COUNTY: Hedenbergite is an accessory in the iron formation at the Jackson County Iron Mine, near Black River Falls (SE sec. 15 T.21N. R.3W.) It is found here with magnetite, quartz, almandine and a complex assemblage of amphiboles including cummingtonite, grunerite and ferroactinolite. (Jones, 1978).
MARATHON COUNTY: Hedenbergite is reported by (Weidman (1904a and 1907b) from the nepheline syenites of the Stettin Pluton near Wausau. In addition to nepheline it is associated with fayalite, sodalite, aegirine, fluorite and K feldspar. Some specific localities reported by Weidmann are: in sect. 1, 2 and 12 T.29N. R.6E. and in the NE sec. 29 T.29N. R.7E.
— Hedenbergite is a component of the quartz syenite pluton exposed at the old Technical Institute in Wausau (SE NE sec. 35 T.21N. R.7E) where it occurs with quartz, microperthite, barkevikite, fayalite and fluorite. (LaBerge and Myers, 1983).