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 …
Oconto County
Hematite
Formula: Fe2O3 Hexagonal Description: “Needle Ore” hematite, longest needle is about 20 cm long. From Montreal Mine in Iron County, Wisconsin. (Photo by W. Cordua.) Hematite is an extremely common mineral. It can form as a sedimentary precipitate, …
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 …
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 …
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 …
Vesuvianite
Formula: (Ca,Na,vacancy)19(Al,Mg,Fe)13(vacancy,B,Al,Fe)5(Si2O7)4(SiO4)10(OH,F,O)10 Tetragonal Description:Vesuvianite most commonly forms in metamorphosed calc-silicate rocks. OCONTO COUNTY: Vesuvianite reportedly occurs with garnet, scapolite, clinopyroxene, hornblende and plagioclase in the Waupee Formation in the Mountain area. Here it is found as a contact …
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. …
Allanite
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 …
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 …
Scapolite Group
Formula: Na4Al3Si9O24Cl – Ca4Al6Si6O24(CO3) Tetragonal Description: Scapolite is a group of minerals related by complex solid solution substitutions. They are found in a wide range of metamorphic rocks formed both by regional and contact metamorphism. The …