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 …
Oneida County
Ferromanganese Nodules
Formula: Mixture Description: Ferromanganese nodules similar to those found on the deep sea floor occur in several lakes in Wisconsin, including Lake Michigan. They consist of a mixture of manganese oxides, iron oxides, sand and clay. …
Tetrahedrite-tennantite
Formula: (Cu,Fe,Ag,Zn)12(Sb,As)4S13 Isometric Description:Tetrahedrite forms a solid solution series with tennantite and freibergite in moderate to low temperature hydrothermal deposits. DOUGLAS COUNTY: Irving (1882) reports finding tetrahedrite in “small quantities in traverse veins in copper-bearing rocks”. This occurrence …
Pyrite
Pyrite is the most common sulfide found in many environments. It is a common accessory mineral in igneous, sedimentary and metamorphic rocks. It also is abundant in most hydrothermal deposits. Only the most significant occurrences …
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 …
Tremolite
Formula: Ca2Mg5Si8O22(OH)2 Monoclinic Description: Tremolite marble from Florence County, Wisconsin. Field of view 7 cm across. (Photo by Al Falster.) Tremolite is formed by the metamorphism of calcium-rich rocks such as limestone and dolostone. It occurs in numerous …
Talc
Formula: Mg3Si4O10(OH)2 Triclinic Description: Talc with pen for scale. From the mineral collection of Brigham Young University Department of Geology, Provo, Utah, Mineral Specimens 1073. Courtesy of the U.S. Geological Survey Denver Library Photographic Collection. (Photo by Andrew …
Actinolite
Formula: Ca2(Mg,Fe)5Si8O22(OH)2 Monoclinic Description: Actinolite is a common member of the amphibole family. It typically forms during low-grade metamorphism of mafic igneous rocks (such as basalt and gabbro) or carbonate-rich rocks such as limey mudstones. ASHLAND COUNTY: Van …
Biotite Group
Formula: K(Mg,Fe)3(Al,Fe3+)Si3O10(OH,F)2 Monoclinic Description: Biotite refers to a group of common rock-forming minerals forming a series between phlogopite and annite. The name is best used as a field name for dark micas for which the exact composition …
Stilpnomelane
Formula: (K,Ca,Na)(Fe, Mg,Al)8(Si,Al)12(O,OH)36.nH2O Triclinic Description: Stilpnomelane is a brown micaceous to velvety to fibrous mineral found in various metamorphic rocks, especially those rich in iron. It often occurs with chlorite, epidote, magnetite, hematite and goethite and …