Formula: (Ce,Ca,Ce,La,Nd,Y)2(Al,Fe)3(Si2O7)(SiO4)O(OH) Monoclinic Description:Allanite refers to a group of minerals found as an accessory in a number of different rocks such as syenite, granite and gneiss. It may also be a component of granite pegmatite. It …
Shawano County
Augite
Formula: (Ca,Na)(Mg,Fe,Al,Ti)(Si,Al)2O6 Monoclinic Description: Augite is the most common mineral in the pyroxene family. It has many varieties due to the variation in chemistry possible in its complex coupled solid solution series. Augite is common in gabbroic …
Bertrandite
Formula: Be4Si2O7(OH)2 Orthorhombic Description: Bertrandite twin, Nine Mile pluton, near Wausau, Marathon County, Wisconsin. Scanning electron microscope image. (Photo by Al Falster.) Bertrandite is a rare mineral found in beryllium rich pegmatites and hydrothermal veins. MARATHON COUNTY: Relatively common …
Beryl
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 …
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 …
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. …
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 …
Copper
Formula: Cu Isometric Description: Native copper occurs as veins and cavity fillings in hydrothermally altered basaltic igneous rocks. It is also a product of near-surface supergene alteration of other copper minerals, such as chalcopyrite. Copper can …
Cummingtonite
Formula: (Mg,Fe)7Si8O22(OH)2 Monoclinic Description: Cummingtonite is a member of the amphibole family. It commonly forms elongated to fibrous green to brown grains in metamorphosed iron-rich rocks. ASHLAND COUNTY: Cummingtonite is found in the Ironwood Iron Formation where it …
Gadolinite-(Y)
Formula: Y2Fe2+Be2Si2O10 Monoclinic Description: Gadolinite-(Y) is an extremely rare mineral found in certain complex granitic pegmatites. SHAWANO COUNTY: Black to dark green anhedral masses of gadolinite up to several cm. in diameter are found in the complex pegmatite …