These concentrates are significantly radioactive. Zircon is a common accessory in the Neillsville augen gneiss exposed along the Black river in NW NW sec. Zircon is common as an accessory mineral in the McCaslin quartzite exposed within Forest and adjacent Langlade, Marinette and Oconto Counties. The zircons are somewhat radioactive. Zircon occurs in a subsurface, diamond-bearing lamprophyre diatreme, discovered within the outskirts of Kenosha.
Zircon is common in many of the igneous rocks of the Wausau area.
The zircon can be brown, yellow, red, pink, cloudy gray and white. Halos formed by the decay of radioactive elements within the zircon often are seen in the surrounding feldspar. Fluorite, siderite, ilmenite, pyrochlore, rutile, anatase and brookite are frequently associated minerals. Some of these rocks are pegmatitic and provide euhedral dipyramidal crystals up to 2 cm. Colors reported are brown, yellow, clear, red or lilac.