Formula: Be3Al2Si6O18 Hexagonal
Description: Beryl is most frequently found in granite pegmatites. It may also be found occasionally in metamorphic rocks such as schists, gneisses and marbles.
EAU CLAIRE COUNTY: Beryl is in “large crystals” from a micaceous pegmatite in the Little Falls area of the Eau Claire River (Myers et al., 1974).
FLORENCE COUNTY: Pale yellow beryl crystals several centimeters long were found in a float boulder of granitic pegmatite in Section 22 T.39N. R.17E near the Pine River, north of Fern (Koehler, 1988). Small (1 cm) beige subhedral crystals were found in a pegmatite dike in NE NE NW Sec. 22 T39N R17E (Koehler, 1989). They were associated with quartz, spodumene and polylithionite (formerly called zinnwaldite). Also beige masses of beryl up to 1.5 x 1.0 cm were found in a pegmatite dike at SE SE SW Sec. 22 T39N R17E with elbaite, columbite-tantalite, triphyllite, muscovite, microcline, albite, and other minerals (Koehler, 1989 personal communication).
MARATHON COUNTY: Reported as a rare constituent of partly assimilated masses of felsic rocks that have been immersed in the magmas of the Wausau pluton (Falster, 1981). Pale blue beryl crystals up to 2 cm were found in a pocket in a pegmatite in quartz syenite, with phenakite crystals. The pocket was found just north of County N, near Rib Mountain (Falster, 1977; Falster et al., 2000).
MARINETTE COUNTY: A matrixless pale blue crystal of beryl labeled “from Middle Inlet” is in the UW–River Falls collection (RF-W-2457).
SHAWANO COUNTY: Euhedral to subhedral crystals several centimeters long ranging in color from yellow to yellow-green to dark green are found in a complex pegmatite near the Embarass River south of the Tigerton Dells, near Tigerton at NE 1/4 SW 1/4 NE 1/4 Sec. 15 T26N R12E. Associated minerals include blue-green potassium feldspar, quartz, bertrandite, and phenakite (WGNHS files, 1986; Falster, 1987).