Formula: MoS2 Hexagonal Description: Molybdenite is a relatively common hydrothermal mineral. It is most often found in vein complexes associated with granitic igneous rocks and related skarns that form at medium to high temperatures. It is economically …
Marathon County
Monazite
Formula: (Ce,La,Nd,Th)PO4 Monoclinic Description: Monazite refers to a group of minerals dominated by various rare earth elements. These minerals commonly form reddish brown to yellowish tabular crystals and granular masses in granitic rocks and placer deposits derived …
Montmorillonite
Formula: (Na,Ca)0.33(Al,Mg)2(Si4O10)(OH)2.nH2O Monoclinic Description: Montmorillonite with pen for scale. From the mineral collection of Brigham Young University Department of Geology, Provo, Utah, Mineral Specimens 794. Courtesy of the U.S. Geological Survey Denver Library Photographic Collection. (Photo by …
Muscovite
Formula: KAl2(AlSi3)O10(OH,F)2 Monoclinic Description:Muscovite is a common mica, forming silvery to pale-colored flakes most commonly schists and granite pegmatites. It can survive weathering, and form sparkling grains in sands and sandstone. Muscovite. From the mineral collection of …
Natrolite
Formula: Na2Al2Si3O10.2H2O Orthorhombic Description: Natrolite is a member of the zeolite family that occurs most frequently in veins and as amygdule fillings in basaltic rocks. BAYFIELD COUNTY: Thin veins of coarsely fibrous radiating clusters of white natrolite …
Nepheline
Formula: (Na,K)AlSiO4 Hexagonal Description: Weathered surface of the same specimen, showing gray pits and hollows where the nepheline has weathered out faster than the surrounding minerals. Green areas are lichen. From the Stettin area, Marathon County, Wisconsin. (Image …
Olivine
Formula: (Mg,Fe)2SiO4 Orthorhombic Description: Olivine is here used to refer to a solid solution series of minerals ranging from the magnesium end member (forsterite) to the iron end member (fayalite). Olivine is widespread in basalts and gabbros, …
Opal
Formula: SiO2.nH2O Amorphous Description: Opal is a mineraloid composed of spherical silica aggregates with various amounts of interstitial water. It forms under a wide range of low-temperature geological conditions. Opal may be deposited by silica secreting …
Pipestone
Formula: Mixture of pyrophillite and sericite. Description:Pipestone is a compact pink to red metamorphosed mudstone (or argillite) of a consistency that allows it to be carved into pipes and other art objects. It is found as thin …
Plagioclase
Formula: CaAl2Si2O8 Triclinic Description: Plagioclase is a family of feldspar minerals forming a solid solution that ranges, relatively continuously, from pure sodium aluminum silicate (the end member called albite) to pure calcium aluminum silicate (the end member …