Formula: Cu3AsS4 Orthorhombic Description: Enargite is a rare hydrothermal mineral found associated with other copper minerals. FOREST COUNTY: Small grains of enargite occur with bornite and digenite replacing chalcopyrite at the Crandon deposit near Little Sand Lake. (Lambe …
Grant County
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 …
Greenockite
Formula: CdS Hexagonal Description: Greenockite is a bright yellow mineral formed by hydrothermal fluids. In Wisconsin it is rarely found associated with sphalerite in the deposits of the Upper Mississippi Valley zinc-lead district. GRANT COUNTY: Occurs at …
Hemimorphite
Formula: Zn4Si2O7(OH)2.H2O Orthorhombic Description: Hemimorphite forms from the breakdown of sphalerite and other zinc minerals. It is common in the oxidized and supergene zones over hydrothermal deposits, where it is associated with smithsonite. Heyl et al. (1959) …
Hydrocarbons
Formula: Mixtures Description: Solid hydrocarbons, generally unanalyzed in detail, are found at a number of localities within the Paleozoic rocks around the state. They may be alternately described as “bitumen” or “asphaltum”. These usually occur as …
Hydrozincite
Formula: Zn5(CO3)2(OH)6 Monoclinic Description: Hydrozincite forms white earthy massive to reniform to stalactitic growths due to the alteration of sphalerite and other zinc minerals by ground water. It is likely quite common (but not often reported) in …
Malachite
Formula: Cu2(CO3)(OH2) Monoclinic Description: Malachite is a common alteration product of other copper-bearing minerals. Its bright green color makes it not only easily recognized, but also highly sought after by mineral collectors. It occurs most notable …
Marcasite
Formula: FeS2 Orthorhombic Description: Marcasite helectite, New Diggings area, Lafayette County, Wisconsin. Sample is about 8 cm long. (Photo by W. Cordua.) Marcasite is common in Wisconsin, often found in well-formed crystals in cavities and veins in the …
Millerite
Formula: NiS Hexagonal Description: Millerite is a low temperature hydrothermal mineral found in vugs in carbonate rocks and as an alteration product of other nickel minerals. Millerite typically forms long brassy fibers making very aesthetic specimens. …