Formula: (Y,U)(Ti,Nb)2O6 Orthorhombic Description: Polycrase-(Y) is a rare black metallic mineral found as flattened prismatic crystals or masses in chemically complex pegmatites. MARATHON COUNTY: Small grains of polycrase (Y) occur in pegmatite at the Koss Pit several miles …
Marathon County
Polylithionite
Formula: KLiFe2+Al(AlSi3O10)(F,OH)2 Monoclinic Description:Polylithionite refers to a dark lithium-rich mica, often an unusual brown, found in some granitic pegmatites. “Zinnwaldite” is a technically discredited name that appears in older literature and refers to this mineral.FLORENCE COUNTY: Koehler (1989) …
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 …
Prosopite
Formula: CaAl2(F,OH)8 Monoclinic Description: Prosopite is a very rare mineral found in fluorine-enriched pegmatites, greisens and carbonatite. MARATHON COUNTY: Prosopite was found as tiny grains (300 microns) with cassiterite, topaz and quartz in a greisen zone in the …
Pseudobrookite
Formula: Fe2TiO5 Orthorhombic Description: Pseudobrookite is a rare mineral occurring in cavities in granitic, rhyolitic, basaltic and other igneous rocks. Marathon County: Pseudobrookite occurs in small prismatic crystals in a vein with quartz, fluorite and pyrite cutting …
Psilomelane
Formula: Mixture of hydrate manganese-barium oxides Description: Psilomelane is used as a blanket term to denote a variety of hard massive mixtures of manganese oxides. Most, but not all, psilomelane is the mineral romanechite (BaMn2+Mn4+8O16(OH)4 ). The …
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 …
Pyrochlore Group
Formula: (Ce, Ca, Y)2Nb2O6(OH,F) Isometric Description: Pyrochlore is a group of rare minerals found in pegmatitic granites, syenites, and carbonatites. MARATHON COUNTY: Pyrochlore group mineral can be found as tiny grains in the Stettin Pluton and Nine-Mile …
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 …
Rhabdophane Group
Formula: (Nd,Ce,La)PO4•H2O Hexagonal Description: Rhabdophane in elongated crystals from the Nine Mile Pluton near Wausau in Marathon County, Wisconsin. Scanning electron microscope image. (Photo by Al Falster.) Rhabdophane-(Ce) from the Nine Mile Pluton near Wausau in Marathon …