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, …
Pierce County
Calcite
Formula: CaCO3 HEXAGONAL Description: Calcite sceptor crystals from Shullsburg, Wisconsin. UW–River Falls specimen. Sample is about 8 cm high. (Photo by Pete Rodewald.) Calcite is an abundant mineral found in many geological environments. It forms by precipitation from …
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 …
Copper
Formula: Cu Isometric Description: Copper wire on gossan, Flambeau Mine, Ladysmith, Rusk County, WI. The wires are a few mm long. (Photograph and specimen by Pete Rodewald) Native copper occurs as veins and cavity fillings in hydrothermally …
Reidite
Formula: ZrSiO4 Tetragonal Description:Reidite, a polymorph of zircon, is an extremely rare mineral that forms under very high pressures, such as are associated with large extraterrestrial impact structures (meteor craters). PIERCE COUNTY: Reidite has been documented by electron …
Potassium Feldspar
Formula: KAlSi3O8 Monoclinic or Triclinic Description: Potassium feldspar refers to any of the three polymorphs microcline, orthoclase or sanidine. The distinction between these minerals can be made with certainty only after detailed X-Ray analysis. This has not …
Tourmaline Group
Formula: Na(Al,Fe,Li,Mg,Mn)3(Al,Cr,V,Fe)6(BO3)3Si6O18(O,OH,F)4 Hexagonal Description: Tourmaline var elbaite Animikie Red Ace pegmatite (red) showing comb texture in pegmatite wall zone. With altered Cs-beryl (yellow-green). Near Fern, Florence County, Wisconsin. (Photo by Al Falster.) Tourmaline is a complex group of …
Dolomite
Formula: CaMg(CO3)2 Hexagonal Description: Dolomite forms the main mineral in the bluff-forming rocks along the Mississippi River, such as Granddad Bluff near La Crosse. (Photo by W. Cordua) Dolomite is an abundant mineral in Wisconsin. It is a …
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 …