Formula: (Fe,Mn)(Nb,Ta)2O6 Orthorhombic Description: Columbite-(Fe) in tabular crystal from the Nine Mile pluton near Wausau in Marathon County, Wisconsin. Scanning electron microscope image. (Image courtesy Al Falster.) Columbite-tantalite refers to a group of minerals having varying amounts …
Wood County
Dolomite
Formula: CaMg(CO3)2 Hexagonal Description: Dolomite forms the main mineral in the bluff-forming rocks along the Mississippi River, such as Granddad Bluff near La Crosse. (Image courtesy W. S. Cordua.) Dolomite is an abundant mineral in Wisconsin. 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 …
Fluorite
Formula: CaF2 Isometric Description: Fluorite crystals, from Sturgeon Bay in Door County, Wisconsin. Field of view is about 4 cm. (Image courtesy W. S. Cordua.) Fluorite often forms coarse cleavable masses or cubic crystals. It can take …
Galena
Formula: PbS Isometric Description: Galena crystals surrounded by marcasite, from Shullsburg, Wisconsin. (Image courtesy W. S. Cordua.) Galena is formed in a wide range of hydrothermal environments. It can be found with sphalerite and chalcopyrite in …
Goethite
Formula: FeO(OH) Orthorhombic Description: Stalactitic goethite from Montreal Mine in Iron County, Wisconsin. (Image courtesy W. S. Cordua.) Goethite is a common iron mineral. It often forms by weathering of other iron-rich minerals, thus is a …
Grossular
Formula: Ca3Al2(SiO4)3. Isometric Description: Grossular is a member of the garnet family found as pale white, green or tan crystals, most often in marbles, calc-silicate and other metamorphic rocks formed from calcium rich protoliths. MARATHON COUNTY: Small …
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 …
Kaolinite
Formula: Al2Si2O5(OH)4 Triclinic Description: Kaolinite with pen for scale. From the mineral collection of Brigham Young University Department of Geology, Provo, Utah, Mineral Specimens 689. Courtesy of the U.S. Geological Survey Denver Library Photographic Collection. (Photo by Andrew …
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 …