Formula: (Ce,Ca,Ce,La,Nd,Y)2(Al,Fe)3(Si2O7)(SiO4)O(OH) Monoclinic Description:Allanite refers to a group of minerals found as an accessory in a number of different rocks such as syenite, granite and gneiss. It may also be a component of granite pegmatite. It …
Oconto County
Andalusite
Formula: Al2SiO5 Orthorhombic Description: Andalusite is found in phyllites, schists and gneisses and associated quartz veins. It indicates relatively low pressure metamorphism of aluminum-rich rocks, such as shales. ASHLAND COUNTY: Andalusite occurs as “chiastolite” in fine-grained schists outcropping …
Andradite
Formula: Ca3Fe2(SiO4)3 Isometric Description: Andradite is a member of the garnet group found in calcareous metamorphic rocks, especially marbles and skarns. FOREST COUNTY: Small grains of andradite, usually with chlorite rims occur in outcrops of the McCaslin …
Chlorite Group
Formula: (Al, Fe, Li, Mg, MN, Ni, Zn)6 (Si, Al)4O10(OH, O)2 MONOCLINIC or TRICLINIC Description: Chlorite represents a group of over 10 minerals related by complex solid solution substitutions. These minerals are generally fine-grained, micaceous and dark green. …
Clinozoisite
Formula: Ca2Al3(Si2O7)(SiO4)O(OH) Monoclinic Description: Common in low-grade metamorphic rocks, particularly as an alteration product of plagioclase. ASHLAND COUNTY: Formed as an alteration product of plagioclase in the gabbros near Mellen, where it forms with epidote, zoisite, calcite …
Cummingtonite
Formula: (Mg,Fe)7Si8O22(OH)2 Monoclinic Description: Cummingtonite is a member of the amphibole family. It commonly forms elongated to fibrous green to brown grains in metamorphosed iron-rich rocks. ASHLAND COUNTY: Cummingtonite is found in the Ironwood Iron Formation where it …
Epidote
Formula: Ca2(Al2Fe3+)(Si2O7)(SiO4)O(OH)2 Monoclinic Description: Epidote is a common mineral formed during low grades of metamorphism and hydrothermal activity. It is particular common in metamorphosed basalts and gabbros where it replaces plagioclase, pyroxene and olivine. It can also …
Gedrite
Formula: (Mg2)(Mg3Al2)(Al2Si6O22)(OH)2 Orthorhombic Description: Gedrite is a member of the amphibole group. It forms during medium to high grade regional metamorphism of ultramafic, iron-rich or clay-rich protoliths. JACKSON COUNTY: Gedrite has been reported intergrown with cummingtonite in the …
Hematite
Formula: Fe2O3 Hexagonal Description: “Needle Ore” hematite, longest needle is about 20 cm long. From Montreal Mine in Iron County, Wisconsin. (Image courtesy W. S. Cordua.) Hematite is an extremely common mineral. It can form as a …
Hornblende
Formula: (Ca,Na)(Mg,Fe)4Al(Si7Al)O22(OH,F)2 Monoclinic Description: Hornblende as a mineral name has been recently discredited. Here it is used as a field name for any dark amphibole for which the exact composition has not been determined. In the past …