Formula: (Fe,Mg,Mn)Al2(SiO4)O(OH)2 Monoclinic Description: Chloritoid forms small green platy to micaceous grains in rocks that have been subjected to moderate grades of regional metamorphism. It may also form by hydrothermal alteration of rocks. It occurs with muscovite, …
Oneida County
Phlogopite
Formula: KMg3(AlSi3O10)(OH)2 Monoclinic Description: Phlogopite is a tan mica found most often in magnesium-rich rocks such as marbles, calc-silicate and ultramafic rocks. KENOSHA COUNTY: Phlogopite occurs in a subsurface, diamond-bearing lamprophyre diatreme, discovered within the outskirts of Kenosha …
Silver
Formula: Ag Isometric Description:Native silver is found in hydrothermal veins or, more rarely, as a supergene mineral. It is associated with gold, and a variety of sulfides such as galena, pyrite and acanthite. Major silver mineralization …
Galena
Formula: PbS Isometric Description: Galena crystals surrounded by marcasite, from Shullsburg, Wisconsin. (Photo by W. Cordua.) Galena is formed in a wide range of hydrothermal environments. It can be found with sphalerite and chalcopyrite in massive sulfide …
Cummingtonite
Formula: (Mg,Fe)7Si8O22(OH)2 Monoclinic Description: Cummingtonite is a member of the amphibole family. It commonly forms elongated to fibrous green to brown grains in metamorphosed iron-rich rocks. ASHLAND COUNTY: Cummingtonite is found in the Ironwood Iron Formation where it …
Pyrrhotite
Formula: Fe1-xS Monoclinic Description: Pyrrhotite with pen for scale. From the mineral collection of Brigham Young University Department of Geology, Provo, Utah, Mineral Specimens 867. Courtesy of the U.S. Geological Survey Denver Library Photographic Collection. (Photo by …
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 …