Formula: MnCO3 Hexagonal Description: Rhodochrosite is an attractive pink mineral formed generally by hydrothermal processes associated with igneous activity or the metamorphism of manganese-rich rocks. IRON COUNTY: Rhodochrosite was found at the Montreal Mine as crystals, druses and …
Marathon County
Riebeckite
Formula: Na2(Fe32+3Fe3+2)Si8O22(OH)2 Monoclinic Description: Riebeckite is a sodium-rich member of the amphibole family. It typically forms dark blue elongated to fibrous crystals in highly sodic granites, syenites, iron formations and schists. JACKSON COUNTY: Minor riebeckite occurs in the …
Rutile
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 …
Samarskite-(Y)
Formula: (Y, Fe3+,Fe2+,U, Th, Ca)2(Nb,Ta)2O8 Orthorhombic Description: Samarskite refers to a group of rare oxides found generally as black resinous masses in granitc pegmatites. The decay of radioactive elements in them often renders them metamict. MARATHON COUNTY: Samarskite-(Y) …
Serpentine
Formula: Mg3Si2O5(OH)4 Monoclinic, orthorhombic, hexagonal Description: Serpentine is a family of polymorphs that include the flaky to platy antigorite, massive lizardite and fibrous clinochrysotile, orthochrysotile and parachrysotile. The polymorphs are often intimately intergrown in a particular rocks, …
Siderite
Formula: FeCO3 Hexagonal Description: Siderite forms as a sedimentary precipitate, in hydrothermal veins, in metamorphic rocks formed from such protoliths, and, rarely, in pegmatites. In sedimentary environments it forms in extensive beds of banded iron formations …
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 …
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 low-silica …
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 …
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 …