Formula: Fe2O3 Hexagonal Description: “Needle Ore” hematite, longest needle is about 20 cm long. From Montreal Mine in Iron County, Wisconsin. (Photo by W. Cordua.) Hematite is an extremely common mineral. It can form as a sedimentary precipitate, …
Dodge County
Allophane
Formula: (Al2O3)(SiO2)1.3-2.2.5-3H2O Amorphous Description: Allophane is a clay mineral with the general chemical composition of kaolinite but lacking a crystalline structure. It is formed by the breakdown of other alumino-silicates, such as feldspar, due to weathering …
Waylandite
Formula: BiAl3(PO4)2(OH)6 Hexagonal Description:Waylandite is a dull to glassy white mineral that occurs rarely in pegmatites with other bismuth-bearing minerals.DODGE COUNTY: Waylandite occurs as very tiny crystals in vugs with bismuth, kettnerite and other minerals in pegmatite …
Halloysite
Formula: Al2Si2O5(OH)4 Monoclinic Description: Halloysite is a clay mineral formed by weathering or hydrothermal alteration of other aluminum-rich minerals. It occurs intermixed with kaolin and other clay minerals. Its identification requires x-ray analysis. Many “clay” occurrences within …
Pyrite
Pyrite is the most common sulfide found in many environments. It is a common accessory mineral in igneous, sedimentary and metamorphic rocks. It also is abundant in most hydrothermal deposits. Only the most significant occurrences …
Calcite
Formula: CaCO3 HEXAGONAL Description: Calcite sceptor crystals from Shullsburg, Wisconsin. UW–River Falls specimen. Sample is about 8 cm high. (Photo by Pete Rodewald.) Calcite is an abundant mineral found in many geological environments. It forms by precipitation from …
Northupite
Formula: Na3Mg(CO3)2Cl Isometric Description: A rare carbonate mineral found in dry lake sediments and other unusual sedimentary environments. DODGE COUNTY: A grain 0.6 cm. long found in the matrix of the Mayville oolitic iron formation was tentatively …
Copper
Formula: Cu Isometric Description: Copper wire on gossan, Flambeau Mine, Ladysmith, Rusk County, WI. The wires are a few mm long. (Photograph and specimen by Pete Rodewald) Native copper occurs as veins and cavity fillings in hydrothermally …
Stevensite
Formula: (Ca,Na)xMg3-x(Si4O10)(OH)2 Monoclinic Description: Stevensite is a massive white clay mineral. IMA lists its species status as questionable. DODGE COUNTY: A white waxy mineral forming elongated grains in the matrix of the Mayville iron ore was tentatively identified …
Corundum
Formula: Al2O3 Hexagonal Description: Corundum is most famous for its rare colored varieties: the bright red ruby and the deep blue sapphire. More often, it is found as drabber blue to blue-gray crystals. Corundum forms in rocks …