Formula: (Ca,Na)xMg3-x(Si4O10)(OH)2 Monoclinic Description: Stevensite is a massive white clay mineral. IMA lists its species status as questionable. DODGE COUNTY: A white waxy mineral forming elongated grains in the matrix of the Mayville iron ore was tentatively identified …
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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 …
Staurolite
Formula: (Fe,Mg,Zn)2Al9(SiO4)4(OH,O)2 Monoclinic Description: Staurolite forms during the metamorphism of aluminous rocks at intermediate temperatures and pressures. It can form large euhedral crystals in schist, associated with muscovite, biotite, almandine and kyanite. Some crystals show distinctive cross …
Spodumene
Formula: LiAlSi2O6 Monoclinic Description: Spodumene forms large white, pale green or, rarely, pink elongated crystals in complex granitic pegmatites. It is often associated with other lithium-rich minerals. FLORENCE COUNTY: At least three pegmatites in sec. 22 T.39N. …
Spinel
Formula: MgAl2O4 Isometric Description: Spinel is found as an accessory mineral in mafic to ultramafic igneous rocks, in marbles and other metamorphic rocks and as a rare heavy mineral in placer deposits. It is usually in small, …
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 …
Spessartine
Formula: Mn3Al2(SiO4)3 Isometric Description: Spessartine is a member of the garnet family. It is usually red to orange in color and is found generally in granite pegmatites, where it can form large gemmy crystals. It is also …
Sodalite
Formula: Na8Al6Si6O24Cl Isometric Description: Sodalite is a blue to white mineral found in silica-undersaturated igneous rocks and their metamorphosed equivalents. It is never found stably together with quartz, but does occur with nepheline, cancrinite and other …
Smithsonite
Description: Massive to botryoidal smithsonite of a form originally called “dry bone ore” by miners. This was a major zinc ore in the mines of southwestern Wisconsin. From the Little Giant Mine, near Shullsburg, Lafayette …
Silver
Formula: Ag Isometric Description: Native silver is found in hydrothermal veins or, more rarely, as a supergene mineral. It is associated with gold, and a variety of sulfides such as galena, pyrite and acanthite. Major silver …