Formula: TiO2 Orthorhombic
Description: Brookite is a relatively uncommon mineral found as an accessory in a number of igneous and metamorphic rocks including granites, syenites, gneisses, and schists. It may also be formed in hydrothermal veins. It is resistant enough to weathering to survive as a heavy mineral in sediments.
MARATHON COUNTY: Brookite is widespread as black, green, yellow and light brown stubby to platy crystals averaging 1 mm. long in vugs in granite pegmatites of the Wausau pluton. These are exposed in the “rotten granite” quarries such as the Wimmer #3 pit south of Rib Mountain (Falster, 1987; Buchholz 1999b., Falster et al., 2000).
— Reported with anatase from a quarry on Mosinee Hill, NW sec. 26 T.26N. R.7E. (Lloyd Brown, pers. comm.)
— 2011 road construction in Stettin township revealed several small vuggy pegmatites with interesting mineralogy. Anorthoclase, microcline and albite are the main rock forming minerals. Brookite was found as pale blue crystals. Associated minerals are zircon, columbite-(Fe), Ilmenite, cassiterite, pyrochlore-group minerals, pyrite, arsenopyrite, and fluorite (Buchholz, Falster and Simmons, 2012).
WOOD COUNTY: Brookite is rarely found as tan micro-crystals associated with anatase and rutile at the Tork and Haessley Quarries near Wisconsin Rapids (Buchholz, 1996).