Formula: SnO2 Tetragonal
Description: Cassiterite is a dark brown to black minerals found in granite pegmatites and high temperature hydrothermal deposits. It may also occur as a heavy mineral in alluvium.
FOREST COUNTY: Cassiterite is reported as tiny grains in several small pegmatites along state highway 55 south of Alvin. (T. Buchholz, 2003, pers. com.)
MARATHON COUNTY: Cassiterite is found as rare small black masses 500 microns in diameter in pegmatites at the Koss Pit (SW sec. 2 T.27 N. R.5E.) SW of Rib Mountain. (Buchholz, Falster and Simmons, 1999, 2000).
Cassiterite is found as very rare overgrowths on ilmenite in pegmatites at the Wimmer Pit #3 (NW sec. 19 T.28N R.7E.) S of Rib Mountain. (Buchholz and Simmons, 2002).
— Minute quantities of cassiterite occur along a quartz vein cutting Ninemile granite Red Rock S.W. (= “Roehl West Quarry”) Quarry , west of Wausau, along Spring Brook Road. (Buchholz and Simmons, 2002) In the adjacent Maguire Pit cassiterite occurs as “dark red brown and masses to 3 mm” associated with topaz, ferberite/hubnerite and other rare minerals. (Buchholz et al., 2004).
— 2011 road construction in Stettin township revealed several small vuggy pegmatites with interesting mineralogy. Cassiterite was found in them as small grains with zircon, columbite-(Fe), Ilmenite, brookite, pyrochlore-group minerals, pyrite, arsenopyrite, and fluorite. ( Buchholz, Falster and Simmons, 2012)
WOOD COUNTY: Cassiterite is found as rare small euhedral crystals on chlorite in quartz veins cutting granite in the John Cepress Quarry (sec. 2 T.23 N. R.2E.) (Buchholz, pers. com., 2000). – Cassiterite occurs as 7-8 micron diameter crystals associated with thorite and allanite (?) in granite in the County Quarry, in Cary township (NW sec. 1 T. 23N R.2E). (Buchholz, pers. comm., 2002).