Formula: CaMg(CO3)2 Hexagonal Description: Dolomite forms the main mineral in the bluff-forming rocks along the Mississippi River, such as Granddad Bluff near La Crosse. (Image courtesy W. S. Cordua.) Dolomite is an abundant mineral in Wisconsin. It …
Bayfield County
Epidote
Formula: Ca2(Al2Fe3+)(Si2O7)(SiO4)O(OH)2 Monoclinic Description: Epidote is a common mineral formed during low grades of metamorphism and hydrothermal activity. It is particular common in metamorphosed basalts and gabbros where it replaces plagioclase, pyroxene and olivine. It can also …
Gold
Formula: Au Isometric Description:Gold is usually found in hydrothermal deposits where it forms at a wide range of temperatures and geological settings. Gold may form in exhalative deposits formed on the sea floor associated with Archean …
Heulandite
Formula: (K,Na,Ca,Sr)2-3Al3(Al,Si)2Si13O36.12H2O Monoclinic Description: Heulandite is a member of the zeolite group usually formed under burial or low temperature metamorphic conditions in mafic igneous or sedimentary rocks. BAYFIELD COUNTY: Heulandite is reported from amygdules in Keweenawan basalt …
Laumontite
Formula: CaAl2Si4O12.4H2O Monoclinic Description: Laumontite is a member of the zeolite family and occurs most frequently in veins and amygdule fillings in basaltic rocks. The mineral forms as the rocks are subjected to heating during relatively …
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 …
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 …
Pectolite
Formula: NaCa2(HSi3O9) Triclinic Description: Pectolite usually forms from hydrothermal fluids as a vein or amygdule filling in basaltic volcanic rocks. It may also form in silica poor syenites and marbles. BAYFIELD COUNTY: Pectolite occurs as white fibers …
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 …