Formula: S Orthorhombic
Description: Sulfur forms around volcanic fumaroles, in sedimentary rocks as a result of bacterial reaction with sulfides and sulfates, and during weathering of sulfides. The sulfur in Wisconsin all occurs as powdery material in cavities, along joints or intergrown with sulfates formed by the weathering of marcasite, pyrite and galena. It apparently is a widespread but not spectacular mineral found throughout the Upper Mississippi Valley zinc-lead district in Iowa and Lafayette Counties. A word of caution: some minerals, such as jarosite, often formed in this environment are also bright yellow and can be easily mistaken for sulfur. The ease with which sulfur fuses is a good test for this mineral.
IOWA COUNTY: Sulfur occurs as efflorescences on and yellow impurities in calcite from the mines near Mineral Point. These likely formed from the decomposition of associated marcasite (Raasch, 1924).
LAFAYETTE COUNTY: “Pale yellow transparent sulfur crystals were noted in cavities in galena in old waste piles in the NE SW SW sec. 7 T.1N. R.1E.” near Benton. (Heyl, et. al., 1959).
— Sulfur is reported occurring as sheets at the Buncombe Diggings, near Hazel Green (Strong, 1873).