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 …
Rusk County
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 …
Anhydrite
Formula: CaSO4 Orthorhombic Description: Anhydrite is a relatively common mineral usually formed as a chemical precipitate from saline water in limestone, dolostone, and salt beds. Its presence is obscured by its tendency to dissolve or be altered …
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 …
Aragonite
Formula: CaCO3 Orthorhombic Description: Aragonite forms in low temperature hydrothermal deposits, especially as sinter around hot springs and amygdules in basalts. It also occurs as speleothems, as organic or inorganic precipitates in marine sediments. Finally, it forms …
Arsenopyrite
Formula: FeAsS Monoclinic Description: Arsenopyrite is formed in hydrothermal deposits, especially those formed at medium to high temperatures. It is often associated with other sulfides such as pyrite and chalcopyrite. CLARK COUNTY: Reported from an unspecified locality …
Azurite
Formula: Cu3(CO3)2(OH)2 Monoclinic Description: Azurite is an attractive blue mineral found as a secondary weathering and supergene mineral formed from the alteration of native copper and other copper minerals. It is often found associated with and altering …
Beaverite-(Cu)
Formula: Pb(Fe3+Cu)3(SO4)2(OH)6 Hexagonal Description: Beaverite-(Cu) is a rare secondary mineral found in the oxidized zone over lead-bearing deposits. RUSK COUNTY: Beaverite occurs as in the oxidized zone at the Flambeau Mine, near Ladysmith (Jones, Jones, and LaBerge, 1999).
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 …
Bornite
Formula: Cu5FeS4 Orthorhombic Description: Bornite forms as a primary hydrothermal precipitate or a later supergene replacement mineral. It occurs with other copper minerals such as covellite, malachite and azurite. It is marked by its intense purple to …