Formula: Cu2O Isometric Description: Cuprite, Flambeau Mine, Rusk County, WI. Fibrous chalcotrichite. Vertical field of view is about 0.3 mm. (Image courtesy Dan Behnke, specimen collected by Dan Behnke.) Cuprite generally forms from the alteration of …
Douglas County
Datolite
Formula: Ca(HBSiO5) Monoclinic Description: Datolite is a low temperature hydrothermal mineral found in cavities and veins, especially in basalts and gabbros. DOUGLAS COUNTY: White fine-grained granular aggregates of datolite, reminiscent of those from Michigan’s Keweenaw Peninsula, occur …
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 …
Galena
Formula: PbS Isometric Description: Galena crystals surrounded by marcasite, from Shullsburg, Wisconsin. (Image courtesy W. S. Cordua.) Galena is formed in a wide range of hydrothermal environments. It can be found with sphalerite and chalcopyrite in …
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 …
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 …
Malachite
Formula: Cu2(CO3)(OH2) Monoclinic Description: Malachite is a common alteration product of other copper-bearing minerals. Its bright green color makes it not only easily recognized, but also highly sought after by mineral collectors. It occurs most notable …
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 …
Nickeline
Formula: NiAs Hexagonal Description: Nickeline, also referred to as “niccolite”, is a rare mineral found in high temperature hydrothermal deposits, especially those in mafic igneous rocks. Other nickel minerals, pyrrhotite and chalcopyrite are commonly associated. ASHLAND …
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, …