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 …
Iron County
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 …
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, dark …
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 …
Stilpnomelane
Formula: (K,Ca,Na)(Fe, Mg,Al)8(Si,Al)12(O,OH)36.nH2O Triclinic Description: Stilpnomelane is a brown micaceous to velvety to fibrous mineral found in various metamorphic rocks, especially those rich in iron. It often occurs with chlorite, epidote, magnetite, hematite and goethite and …
Talc
Formula: Mg3Si4O10(OH)2 Triclinic Description: Talc with pen for scale. From the mineral collection of Brigham Young University Department of Geology, Provo, Utah, Mineral Specimens 1073. Courtesy of the U.S. Geological Survey Denver Library Photographic Collection. (Photo by Andrew …
Thomsonite-Ca
Formula: NaCa2Al5Si5O20.6H2O Orthorhombic Description: Thomsonite-Ca is a member of the zeolite group often found in radiating clusters of varying color in the amygdules of volcanic rocks.IRON COUNTY: Thomsonite-Ca occurs abundantly in outcrops of the Porcupine volcanics along …
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 …