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 …
Pierce County
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 …
Platinum
Formula: Pt Isometric Description: Platinum is a rare mineral found in ultramafic rocks or in placers derived from them. PIERCE COUNTY: Small particles of platinum were reportedly found during placer mining operations for gold along Plum Creek …
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 …
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 …
Quartz
Formula: SiO2 Hexagonal Description: Quartz is the most abundant mineral. It is an essential component of granitic igneous rocks, of sedimentary rocks such as sandstone and chert and of metamorphic rocks such as quartzites. It is a …
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 backscatter …
Topaz
Formula: Al2(SiO4)(F,OH)2 Orthorhombic Description: Topaz from the Nine Mile Pluton near Wausau in Marathon County, Wisconsin. Scanning electron microscope image. (Photo by Al Falster.) Topaz forms in granitic pegmatites, in cavities in rhyolitic volcanic rocks and in residual …
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 …