Formula: (Fe,Mg)7Si8O22(OH)2 Monoclinic Description: Grunerite is a member of the amphibole family. It occurs in relatively iron-rich rocks that have been subjected to moderate grades of metamorphism. ASHLAND COUNTY: Grunerite is a widespread contact metamorphic minerals in the …
Iron County
Gypsum
Formula: CaSO4.2H2O Monoclinic Description: Gypsum is a relatively common mineral in a number of environments. It is found in sedimentary rocks, either as a primary precipitate from sea or saline lake waters or as a alteration …
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 …
Kyanite
Formula: Al2SiO5 Triclinic Description: Kyanite schist outcrop near Powell in Iron County, Wisconsin. (Photo courtesy Tod Roush.) Kyanite is formed by the metamorphism of aluminum-rich rocks, and is often associated with biotite, muscovite, almandine, staurolite, and sillimanite. It …
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 …
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 …
Manganite
Formula: MnO(OH) Monoclinic Description: Manganite is a lustrous black to steel gray mineral formed in hydrothermal veins or as a groundwater precipitate. IRON COUNTY: Manganite was found as lustrous striated tabular crystals in clusters lining vugs up …
Minnesotaite
Formula: (Fe,Mg)3Si4O10(OH)2 Triclinic Description: Minnesotaite is found frequently as small grains in iron formations that have experienced low grade metamorphism. It is often associated with stilpnomelane, cummingtonite, chlorite and siderite. Wisconsin localities for this minerals are restricted …
Monazite
Formula: (Ce,La,Nd,Th)PO4 Monoclinic Description: Monazite refers to a group of minerals dominated by various rare earth elements. These minerals commonly form reddish brown to yellowish tabular crystals and granular masses in granitic rocks and placer deposits derived …