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 …
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Siegenite
Formula: (Co,Ni)3S4 Isometric Description: Siegenite is an uncommon sulfide of nickel and cobalt found in hydrothermal deposits. WOOD COUNTY: Siegenite has been identified by XRD and EDS analysis of small gray metallic xls. found at the Frederick Schill …
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 …
Sicklerite
Formula: Li(Mn,Fe)PO4 Orthorhombic Description: Sicklerite is a rare yellowish to dark brown phosphate formed as a result of the alteration of other phosphate minerals in granite pegmatites. FLORENCE COUNTY: Sicklerite has been tentatively identified as a coating on …
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, …
Scheelite
Formula: CaWO4 Tetragonal Description: Scheelite is a high temperature hydrothermal mineral that forms the primary ore of tungsten. WOOD COUNTY: Scheelite occurs rarely as “tiny grayish crystals” in quartz with molybdenite in the Haessley Quarry, Wisconsin Rapids, Wisconsin. …
Scapolite Group
Formula: Na4Al3Si9O24Cl – Ca4Al6Si6O24(CO3) Tetragonal Description: Scapolite is a group of minerals related by complex solid solution substitutions. They are found in a wide range of metamorphic rocks formed both by regional and contact metamorphism. The …
Sauconite
Formula: Na0.3Zn3(Si,Al)4O10(OH)2.4H2O Monoclinic Description: Sauconite is a zinc-rich clay mineral formed by alteration of sphalerite. It is probably widespread, but under-recognized, in the many mines of the Upper Mississippi Valley zinc-lead district. LAFAYETTE COUNTY: Sauconite is found …
Saponite
Formula: Ca0.25(Mg,Fe)3(Si,Al)4O10(OH)2.nH2O Monoclinic Description: Saponite is a clay mineral most often found as an amygdule filling in volcanic rocks. DOUGLAS COUNTY: Saponite is reported as occurring in the amygdules of basaltic volcanic rocks exposed along the Black …
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) …