Formula: FeTiO3 Hexagonal
Description: Ilmenite is a black metallic mineral occurring in tabular crystals or platy masses. It is found as an accessory mineral in many rocks, particularly gabbro and anorthosite. It can be found as a heavy mineral in detrital sediments, although it does alter readily to a mixture of white to yellow titanium oxides known collectively as leucoxene. Ilmenite is probably much more common in the state than the localities below indicate. It is easily overlooked or, because of its weak magnetic properties mistaken in small grains for magnetite.
ASHLAND COUNTY: Ilmenite mixed with magnetite make up nearly 60% of the rock in some drill core through gabbroic rocks near Clam Lake (Dugan and Ervin, 1977).
— Coarse ilmenite occurs in anorthositic gabbro and gabbro pegmatite in the quarry on Quarry road at NW NW Sec. 4 T.44N R.3W west of Mellen. It also occurs at a quarry near Loon Lake in the SE Sec. 29 T.45N R.2W (Cordua, field notes).
DODGE COUNTY: Tiny black platey grains were seen in pegmatites cutting quartzite in the Michels Materials Waterloo Quarry, NE sec. 33 and NW sec. 34 T.9N. R.13E. (Buchholz et al. , 2003)
KENOSHA COUNTY: Picro-ilmenite and chrome ilmenite occur in a subsurface, diamond-bearing lamprophyre diatreme, discovered within the outskirts of Kenosha. (Carlson and Adams, 1997.).
MARATHON COUNTY: Solution-etched platy crystals of ilmenite up to 1 cm. across are found in the cavities of the rocks of the Wausau pluton, such as are exposed in the rotten granite quarries south of Rib Mountain (Falster, 1987; Falster et al., 2000).
— Ilmenite occurs in platy crystals, now mostly leucoxene, in mariolitic cavities at the Wimmer Pit #3, where it is associated with anatase, zircon, goethite, fluorite and apatite (Buchholz, 1993, personal communication).
— Ilmenite occurs in platy crystals, now mostly leucoxene, in mariolitic cavities at the Koss Pit #3 (Buchholz, 1993, personal communication).
— Ilmenite is found as platy crystals partly replaced by leucoxene in vugs in syenite at the old thorium mine near Stettin. (Buchholz, 1994, personal communication). Ilmenite also occurs in massive form in the pegmatites in this pluton (Falster, et al., 2000).
SHAWANO COUNTY: Ilmenite is locally abundant in the Tigerton Anorthosite found exposed throughout western Shawano County. It is associated with coarse plagioclase, hornblende, biotite and magnetite. Enough ilmenite and magnetite may be present locally as to affect a compass needle. Some outcrops of anorthosite bearing ilmenite are in SW NE sec. 33 T.28N. R.11E. near Shepley, SW SW sec. 23 T.27N. R.12E. where County J crosses the Middle Branch of the Embarass River, and SE SE sec. 36 T.28N. R.12E. south of Bowler (Institute of Lake Superior Geology, 1973; Greenberg et al., 1986).
WAUPACA COUNTY: Ilmenite was reported as small tabular crystals in altered biotite from road cuts in pegmatite cutting granite along County G near Keller Lake, NE of Big Falls. Associated minerals include euxenite-(Y), biotite, fluorite, K feldspar, bastnaesite group minerals, allanite and various sulfides. (Tom Buchholz, 2002, personal communication)