Formula: TiO2 Tetragonal Description: Rutile from the Nine Mile Pluton near Wausau in Marathon County, Wisconsin. Scanning electron microscope image. (Photo by Al Falster.) Rutile is an accessory mineral found in a wide variety of rocks, usually as …
Forest County
Sillimanite
Formula: Al2SiO5Orthorhombic Description: White elongated sillimanite crystals in schist with lustrous grey graphite, white quartz and pink garnet altering to iron oxide. Alder Gulch, near Virginia City, Montana. Field of view is about 0.5 cm left to right. (Photo …
Sphalerite
Formula: ZnS Isometric Description: Banded sphalerite, near Hazel Green in Lafayette County, Wisconsin. Sample is about 1 cm long. Sphalerite occurs in a wide range of hydrothermal environments. It is common with chalcopyrite in exhalative massive …
Stephanite
Formula: Ag5SbS4 Orthorhombic Description: Stephanite is a rare black mineral formed in silver-rich hydrothermal deposits. FOREST COUNTY: Stephanite occurs at the Crandon massive sulfide deposit, near Little Sand Lake. The mineral occurs with polybasite-pearceite and tetrahedrite-tennantite as very …
Tetrahedrite-tennantite
Formula: (Cu,Fe,Ag,Zn)12(Sb,As)4S13 Isometric Description:Tetrahedrite forms a solid solution series with tennantite and freibergite in moderate to low temperature hydrothermal deposits.DOUGLAS COUNTY: Irving (1882) reports finding tetrahedrite in “small quantities in traverse veins in copper-bearing rocks”. This occurrence has …
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 …
Uraninite
Formula: UO2 Isometric Description: Uraninite with pen for scale. From the mineral collection of Brigham Young University Department of Geology, Provo, Utah, Mineral Specimens 1134. Courtesy of the U.S. Geological Survey Denver Library Photographic Collection. (Photo by Andrew …
Zircon
Formula: ZrSiO4 Tetragonal Description: Zircon in tabular crystal from the Nine Mile Pluton near Wausau in Marathon County, Wisconsin. Scanning electron microscope image. (Photo by Al Falster.) Zircon is a common accessory mineral found in many different …