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 …
Iowa 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 …
Halloysite
Formula: Al2Si2O5(OH)4 Monoclinic Description: Halloysite is a clay mineral formed by weathering or hydrothermal alteration of other aluminum-rich minerals. It occurs intermixed with kaolin and other clay minerals. Its identification requires x-ray analysis. Many “clay” occurrences within …
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 …
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) …
Honessite
Formula: Ni6Fe2(SO4)(OH)16.4H2O Hexagonal Description: Honessite is one of a number of secondary nickel sulphates formed by the weathering of primary hydrothermal nickel sulfides such as millerite, violarite or nickeliferous pyrite (so-called “Bravoite”). It is found at …
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 …
Leadhillite
Formula: Pb4(SO4)(CO3)2(OH)2 Monoclinic Description: Leadhillite is a rare mineral found in the oxidized zone of lead deposits, usually associated with anglesite and cerussite. IOWA COUNTY: Irving (1883) reports leadhillite as occurring in the mines in the Mineral Point …
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 …