Formula: Al2SiO5 Orthorhombic
Andalusite is found in phyllites, schists and gneisses and associated quartz veins. It indicates relatively low pressure metamorphism of aluminum-rich rocks, such as shales.
ASHLAND COUNTY: Andalusite occurs as “chiastolite” in fine-grained schists outcropping along the Bad River at Penokee Gap west of Mellen (SW 1/4 Sec. 11 T.44E R3W). The crystals are described as being up to 1 cm. long, and as individuals and “intersecting clusters crowded with inclusions.” They are associated with biotite, quartz, almandine, muscovite, chlorite and pyrite (Van Hise and Irving, 1892).
DODGE COUNTY: Cores taken from a well about 3 km. east of Waterloo contain phyllite with reddish brown subhedral to anhedral andalusite. The andalusite is partly altered to sericite and associated with quartz and muscovite (Smith, 1978). It has subsequently been found as reddish brown xls. several inches long in argillite in east of Portland (SE sec. 33 and SW sec. 34 T.9N. R.13E)(Luther, 1997) and elsewhere in the pelitic rock interlayered with the Waterloo quartzite (Geiger, et al., 1982, Brown et al., 2001).
— Andalusite is common in pelitic rocks associated with quartzite in the Michels Materials Waterloo Quarry, NE sec. 33 and NW sec. 34 T.9N. R.13E. (Buchholz et al. , 2003)
FLORENCE COUNTY: In metasedimentary rocks underlying the Quinnesec Formation in the Dunbar gneiss dome (Schulz and Sims, 1982).
FOREST COUNTY: Observed in the contact metamorphic aureole around the High Falls granite pluton in the McCaslin Range (Olson, 1984).
JACKSON COUNTY: Andalusite is found in several of the rock units at the Jackson County Iron Mine east of Black River Falls (SE 1/4 Sec. 15 T.21N R.3W). Both the hanging wall and footwall schist contain andalusite associated with biotite, muscovite, chlorite, staurolite, almandine and quartz. Andalusite is also reported as crystals up to 1.5 cm. long in a talc schist body associated with anthophyllite, cummingtonite, almandine and kyanite. (Jones, 1978). Kimball and Spear (1984) suggest it forms here as a replacement of earlier formed staurolite.
JEFFERSON COUNTY: Andalusite occurs as porphyroblasts with muscovite in quartzite in the Waterloo area such as “near the nose of the syncline on Glascow’s farm.” (Brandon, et. al., 1980).
LANGLADE COUNTY: Andalusite occurs with staurolite in metapelitic schists near Kempster. Associated minerals are quartz, biotite, muscovite, plagioclase and chlorite (Geiger and Guidotti. 1989).
LINCOLN COUNTY: Andalusite occurs with staurolite in metapelite schist west of Merrill, as at SE Sec. 7 and NE Sec. 18 T.31N R7E. Associated minerals are biotite, muscovite, quartz, chlorite, and garnet (Geiger and Guidotti, 1989).
MARATHON COUNTY: Reported with quartz, kaolinite and pyrophyllite in an argillite exposed on Rib Mountain (Gunderson, 1986).
MARINETTE COUNTY: Andalusite altering to muscovite is found in metasedimentary rocks of the Quinnesec Formation along the South Branch of the Pike River south of Dunbar. Outcrops occur in the SE Sec. 36 T.36N. R18E., and in Sec. 5 and NE Sec. 8 T.35N R.18E. (Cummings, 1978).
—Poikiloblastic andalusite occurs in metaconglomerate on Thunder Mountain Sec. 29, 30, 31 and 32 T.33N R.18E (Murskey, et. al., 1969). Associated minerals are quartz, sillimanite, hematite, and muscovite.
OCONTO COUNTY: Andalusite is associated with sillimanite, mica, quartz and feldspar in the contact zone around the Hager granite in the vicinity of Mountain (Lahr, 1972).
RUSK COUNTY: Schists associated with the massive sulfide Flambeau deposit near Ladysmith contain andalusite as light gray porphyroblasts averaging that can be up to 10 cm. long associated with biotite, chlorite, quartz, pyrite and sericite (May,1977; Cordua, 1994 field obs.).
— Andalusite is a component of the meta-sedimentary rocks at the Eisenbrey massive sulfide deposit north of Ladysmith (NW sec. 17 T.35N. R.6W. (May, 1996).