Opals
DODGE COUNTY: Opal has been found as a microscopic component of the oolites in the
Mayville iron ore (Hawley and Beavan, 1934).
FLORENCE COUNTY: Colorless hyalite opal is found as encrustation on feldspar in
the zoned, lithium-rich pegmatites in sec. 22 T.31N. R.17E. in Fern Township. This
material fluoresces green under short wave ultraviolet light (Koehler, 1988).
JACKSON COUNTY: Common opal is the major component of a bed of diatomaceous
earth in a bed 15 centimeters thick deposited in a Pleistocene lake and now outcropping
near Hixton, N 1/2 SW SE Sec. 17 T.22N R.5W (Andrews, 1966).
MARATHON COUNTY: Hyalite opal encrustations are common in the pegmatites of the
Wausau pluton, such as are exposed in the rotten granite quarries south of Rib Mt. Sec. 19
and 20 T.28N R.7E.
VILAS COUNTY: Bottom mud in a number of county lakes contains diatomaceous earth
sediments. Some lakes containing diatomaceous earth are Alder, Allequash, Big Arbor Vitae,
Found, Little Crooked, Lost Canoe, Mann, Sweeney and Wolff. This material is likely
wide-spread throughout Wisconsin (USGS, 1976).
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