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 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 K-feldspar, quartz, bertrandite and phenakite (WGNHS files, 1986; Falster, 1987).