Formula: Be3Al2Si6O18 Hexagonal Description: Beryl variety aquamarine from the Nine Mile pluton near Wausau in Marathon County, Wisconsin. Scanning electron microscope image. Field of view 2 cm. (Photo by Al Falster.) Beryl is most frequently found in granite …
Florence County
Biotite Group
Formula: K(Mg,Fe)3(Al,Fe3+)Si3O10(OH,F)2 Monoclinic Description: Biotite refers to a group of common rock-forming minerals forming a series between phlogopite and annite. The name is best used as a field name for dark micas for which the exact composition …
Chalcopyrite
Formula: CuFeS2 Tetragonal Description: Chalcopyrite is an important ore of copper found in a wide range of hydrothermal environments. It is often associated with sphalerite and galena. It oxidizes to form copper minerals such as malachite, azurite, …
Chlorite Group
Formula: (Al, Fe, Li, Mg, MN, Ni, Zn)6 (Si, Al)4O10(OH, O)2 MONOCLINIC or TRICLINIC Description: Chlorite represents a group of over 10 minerals related by complex solid solution substitutions. These minerals are generally fine-grained, micaceous and dark green. …
Chloritoid
Formula: (Fe,Mg,Mn)Al2(SiO4)O(OH)2 Monoclinic Description: Chloritoid forms small green platy to micaceous grains in rocks that have been subjected to moderate grades of regional metamorphism. It may also form by hydrothermal alteration of rocks. It occurs with muscovite, …
Clinozoisite
Formula: Ca2Al3(Si2O7)(SiO4)O(OH) Monoclinic Description: Common in low-grade metamorphic rocks, particularly as an alteration product of plagioclase. ASHLAND COUNTY: Formed as an alteration product of plagioclase in the gabbros near Mellen, where it forms with epidote, zoisite, calcite …
Columbite-Tantalite
Formula: (Fe,Mn)(Nb,Ta)2O6 Orthorhombic Description: Columbite-(Fe) in tabular crystal from the Nine Mile pluton near Wausau in Marathon County, Wisconsin. Scanning electron microscope image. (Image courtesy Al Falster.) Columbite-tantalite refers to a group of minerals having varying amounts …
Cordierite
Formula: (Mg,Fe)2Al3(AlSi5O18) Orthorhombic Description: Cordierite is found in many medium-grade metamorphic environments. It is often found in the high temperature-low pressure zones in contact metamorphic halos. In Wisconsin, however, it most often is found in schist …
Diopside
Formula: CaMgSi2O6 Monoclinic Description: Diopside occurs in moderate to high-grade metamorphic rocks. It is particularly common in marbles, calc-silicate rocks, and amphibolites. FLORENCE COUNTY: Found with tremolite in marble from a drill core into a metasedimentary sequence from …
Ferrimolybdite
Formula: Fe2(MoO4)3.n(H2O) Orthorhombic Description: Ferrimolybdite forms yellow earthy to fibrous coatings as a result of the oxidation of molybdenite. FLORENCE COUNTY: Found at the Payant-Chrissman prospect pits in the north central part of sec. 33 T.38N. R.19E, …