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 …
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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 …
Prehnite
Formula: Ca2Al2Si3O10(OH)2 Orthorhombic Description: Prehnite in vug in basalt, with dark marcasite crystals. Buckley quarry, Douglas County, WI. field of view about 6 cm. across. (Photo by W. Cordua) Prehnite is most often found as a vein or …
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 …
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 …
Polycrase-(Y)
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 …
Polybasite-pearceite
Formula: [(Ag,Cu)6(Sb,As)2S7][Ag9CuS4] Monoclinic Description: Polybasite-pearceite are a series of black minerals formed in moderate to low temperature silver-rich hydrothermal deposits. FOREST COUNTY: Polybasite-pearceite are very rare in the Crandon massive sulfide deposit, near Little Sand Lake. The …
Plumbogummite
Formula: PbAl3(PO4)2(OH)5.H2O Hexagonal Description: Plumbogummite is a rare secondary mineral found in the oxidized zone over lead-bearing deposits. RUSK COUNTY: Plumbogummite occurs in the oxidized zone at the Flambeau Mine, near Ladysmith (Jones, Jones, and LaBerge, 1999). …
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 …
Plagioclase
Formula: CaAl2Si2O8 Triclinic Description: Plagioclase is a family of feldspar minerals forming a solid solution that ranges, relatively continuously, from pure sodium aluminum silicate (the end member called albite) to pure calcium aluminum silicate (the end member …