Formula: Ca2(Mg,Fe)5Si8O22(OH)2 Monoclinic Description: Actinolite is a common member of the amphibole family. It typically forms during low-grade metamorphism of mafic igneous rocks (such as basalt and gabbro) or carbonate-rich rocks such as limey mudstones. ASHLAND COUNTY: Van …
Marinette County
Allanite
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 …
Almandine
Formula: Fe3Al2(SiO4)3 Isometric Description: Almandine is a common garnet found in a many metamorphic rocks such as schist, gneiss, amphibolite and iron formation. It is commonly associated with micaceous minerals such as muscovite, biotite and chlorite and …
Andalusite
Formula: Al2SiO5 Orthorhombic Description: Andalusite is found in phyllites, schists and gneisses and associated quartz veins. It indicates relatively low pressure metamorphism of aluminum-rich rocks, such as shales. ASHLAND COUNTY: Andalusite occurs as “chiastolite” in fine-grained schists outcropping …
Anthophyllite
Formula: (Mg,Fe)7Si8O22(OH)2 Orthorhombic Description: Anthophyllite is a mineral formed from the metamorphism of magnesium-rich rocks. It is often associated with other amphibole minerals, pyrope, and cordierite. JACKSON COUNTY: Anthophyllite occurs as long radiating fibrous crystals and masses intergrown …
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 …
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, …