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 …
Lincoln County
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 …
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, …
Orthopyroxene
Formula: (Mg,Fe)SiO3 Orthorhombic Description: Orthopyroxenes are a group of minerals ranging from pure MgSiO3 (enstatite) to pure FeSiO3 (ferrosilite). Bronzite and hypersthene are orthopyroxenes mid-way between these two end members. As the particular orthopyroxene mineral described is not always …
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, …
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 …