Formula: Cu3(CO3)2(OH)2 Monoclinic Description: Azurite is an attractive blue mineral found as a secondary weathering and supergene mineral formed from the alteration of native copper and other copper minerals. It is often found associated with and altering …
Crawford County
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 …
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 …
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, …
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 …
Glauconite
Formula: (K,Na)(Fe3+,Al,Mg)2(Si,Al)4O10(OH)2 Monoclinic Description: Glauconite is abundant in the Paleozoic sandstones in Wisconsin where it forms rounded dark green sand-sized nodules. At places glauconite may make up the majority of the rock, forming what are commonly called …
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 …
Hydromagnesite
Formula: Mg5(CO3)4(OH)2.4H2O Monoclinic Description: Hydromagnesite forms white chalky masses or, occasionally sprays of radiating acicular to bladed crystals due to the alteration and weathering of magnesium-rich rocks. CRAWFORD COUNTY: Hydromagnesite is a major component of moon-milk …
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 …