Formula: Fe2O3 Hexagonal Description: “Needle Ore” hematite, longest needle is about 20 cm long. From Montreal Mine in Iron County, Wisconsin. (Photo by W. Cordua.) Hematite is an extremely common mineral. It can form as a sedimentary precipitate, …
Richland County
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 …
Chalcopyrite
Formula: CuFeS2 Tetragonal Description: Chalcopyrite is an important ore of copper found in a wide range of hydrothermal environments. It is often associated with sphalerite and galena. It oxidizes to form copper minerals such as malachite, azurite, …
Limonite
Formula: Mixture of hydrated iron oxides Description: Limonite is a general term for a mixture of fine-grained iron oxides, generally dominated by goethite, but also possibly containing hematite, lepidochrocite and other minerals. It forms from the …
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 …
Calcite Speleothems
Formula: CaCO3 HEXAGONAL Description: Speleothems are precipitates, usually made of calcite, in caverns. They should be conserved and not be collected from caves in order to preserve the caves’ beauty, interest and scientific values. CRAWFORD COUNTY: Abundant speleothems …
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 …
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 …
Chalcocite
Formula: Cu2S Monoclinic Description: Chalcocite is formed either as a primary vein mineral or, more typically, in supergene deposits where it forms as a result of the redeposition of copper from the breakdown of minerals such …
Goethite
Formula: FeO(OH) Orthorhombic Description: Stalactitic goethite from Montreal Mine in Iron County, Wisconsin. (Photo by W. Cordua.) Goethite is a common iron mineral. It often forms by weathering of other iron-rich minerals, thus is a common component …