Hornblende is a very common mineral found in many geologic environments. It is found in many intrusive igneous rocks ranging in composition from granites to diorite to gabbros to syenites. It occurs as phenocrysts in several varieties of extrusive igneous rocks, such an andesite. It occurs as a detrietal heavy mineral in sedimentary rocks. It forms in a number of gneissic rocks formed at moderate grades of metamorphism.
Amphibolites are common metamorphic rocks consisting in large part of hornblende.
Igneous and metamorphic rocks containing hornblende are widespread throughout Wisconsin's Precambrian shield. Large hornblende crystals are found in a mafic pegmatite dike found about 2 miles north of Mellen in the SW Sec. 32-36 T.45N R.3W and Sec. Hornblende is common as small grains in amphibolites exposed along the Chippewa River near Cornell in the NE Sec. Hornblende is common as small grains with plagioclase in amphibolite at Little Falls at the Hwy.