Formula: Fe3Al2(SiO4)3 Isometric Description: Almandine is a common garnet found in a many metamorphic rocks such as schist, gneiss, amphibolite and iron formation. It is commonly associated with micaceous minerals such as muscovite, biotite and chlorite and …
Iron County
Staurolite
Formula: (Fe,Mg,Zn)2Al9(SiO4)4(OH,O)2 Monoclinic Description: Staurolite forms during the metamorphism of aluminous rocks at intermediate temperatures and pressures. It can form large euhedral crystals in schist, associated with muscovite, biotite, almandine and kyanite. Some crystals show distinctive cross …
Augite
Formula: (Ca,Na)(Mg,Fe,Al,Ti)(Si,Al)2O6 Monoclinic Description: Augite is the most common mineral in the pyroxene family. It has many varieties due to the variation in chemistry possible in its complex coupled solid solution series. Augite is common in gabbroic …
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, …
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 …
Laumontite
Formula: CaAl2Si4O12.4H2O Monoclinic Description: Laumontite is a member of the zeolite family and occurs most frequently in veins and amygdule fillings in basaltic rocks. The mineral forms as the rocks are subjected to heating during relatively …
Calcite
Formula: CaCO3 HEXAGONAL Description: Calcite sceptor crystals from Shullsburg, Wisconsin. UW–River Falls specimen. Sample is about 8 cm high. (Photo by Pete Rodewald.) Calcite is an abundant mineral found in many geological environments. It forms by precipitation from …
Serpentine
Formula: Mg3Si2O5(OH)4 Monoclinic, orthorhombic, hexagonal Description: Serpentine is a family of polymorphs that include the flaky to platy antigorite, massive lizardite and fibrous clinochrysotile, orthochrysotile and parachrysotile. The polymorphs are often intimately intergrown in a particular rocks, …
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 …
Magnetite
Formula: Fe2+Fe3+2O4 Isometric Description: Magnetite is a common mineral found at many localities in Wisconsin. Only localities that where the mineral is present in great abundance or as unusual material are listed here. Magnetite occurs as an …