Formula: ZrSi04 TETRAGONAL
Description: Zircon is a common accessory mineral found in many different rocks. It occurs as small grains in granitic rocks, syenites, schists and gneisses. It may form larger crystals in pegmatitic rocks or marbles. Since it is a dense, reasonably resistant mineral, it can be found in heavy mineral fraction of sedimentary rocks, possibly even in concentrates in placer deposits. Zircon has frequently been noted as in this occurrence in the sediment and sedimentary rocks of the state (Irving, 1883, Ockerman, 1930, Becker, 1931, Tyler, 1940, Davis, 1966). Some zircon contains significant uranium and thorium. The radiation produced by these impurities may damage or destroy zircon’s crystal structure. Zircon can often be spotted when as small grains because of its tendency to fluoresce yellow under short wave ultraviolet light.
ADAMS COUNTY: Tiny zircon crystals are a common accessory in the granitic rocks in the quarry on Hamilton Mounds (SE NE sec. 36 T.20N R6E) (Greenberg et. al., 1986).
ASHLAND COUNTY: Zircon as “large euhedral crystals” are “abundant” in certain granophyre and ferrodiorite bodies within the Mineral Lake Intrusion, near Mellen (Klewin et. al., 1989). Wilcox reports on a more specific locality near Mellen in the SW sec. 29 T.45N. R.2W. where a pegmatite dike contained cinnamon brown zircon crystals up to 18 cm. long by 0.5 cm. in diameter. Th zircon was associated with plagioclase, hornblende and biotite. This is near or at the site of a modern quarry in anorthosite on Loon Lake, near Copper Falls State Park.
BAYFIELD COUNTY: Tiny zircons are the “most common” heavy mineral in the Barron Quartzite in the Blue Hills of Barron and adjacent Rusk County (Razackey, 1987).
CHIPPEWA COUNTY: Zircon and other dense minerals occur in placer-like concentrations in the Flambeau Quartzite, such as is exposed in numerous outcrops in T.32N. R.7W. These concentrates are significantly radioactive. (Campbell, 1981).
CLARK COUNTY: Zircon is a common accessory in the Neillsville augen gneiss exposed along the Black river in NW NW sec. 26 T.24N. R.2W. The zircon occurs as tiny euhedral crystals intergrown with biotite, K feldspar and other minerals (Maas and Van Schmus, 1981).
FOREST COUNTY: 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. (Olson, 1984).
KENOSHA COUNTY: Zircon occurs in a subsurface, diamond-bearing lamprophyre diatreme, discovered within the outskirts of Kenosha. (Carlson and Adams, 1997.).
MARATHON COUNTY: Zircon is common in many of the igneous rocks of the Wausau area.
– Falster (1987, 1989), Falster and Simmons (1989), Buchholz (1999b), and Buchholz, Falster and Simmons (1999) describe zircon as occurring as short prismatic crystals in the “rotten granite” widely exposed in quarries south of Rib Mountain. 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. The zirocn may show Hf enrichment. Zircon can be found at the Koss Pit (SW sec. 2 T27N R.5E), the Red Rock Granite North Pit (along Spring Brook Road), the Ladick Quarry (sec. 19 and 20 T. 27N. R.6E.) and the Wimmer #3 pit (NW sec. 19 T.28N R7E) (Falster, et. al., 2000; Buchholz and Simons, 2002).
-Zircon is common in the syenites of the Stettin pluton where it occurs with K feldspar, fluorite, quartz, and soda-rich amphiboles. Some of these rocks are pegmatitic and provide euhedral dipyramidal crystals up to 2 cm. long (Falster and Simmons, 1989, Falster, et. al., 2000). Colors reported are brown, yellow, clear, red or lilac. Many of the zircons are radioactive. K feldspar, fluorite, aegirine and riebeckite are often associated. Numerous pits and outcrops in T.29N. R.6E. contain zircon-bearing rocks. These are SW sec. 15, NW sec. 22 ; SW NW sec. 23 NE sec. 27(Weidmann, 1907a and b; Vickers, 1956; Stobbe and Murray, 1956). An old quarry where zircon was once mined occurs in the SE SE sec. 22 T.29N R6E where abundant euhedral dipyramidal crystals up to 14 mm. long occur in the weathered granite. Some of the crystals are geniculate twins. (LaBerge and Myers, 1983; Stobbe and Murray, 1956). Zunker’s pit (SW SE sec. 22) is another locality where loose zircon crystals can be found in weathered syenite associated with fluorite, K feldspar and other minerals. (WSC field notes).
-2011 road construction in Stettin township revealed several small vuggy pegmatites with interesting mineralogy. Anorthoclase, microcline and albite are the main rock forming minerals. Associated minerals are zircon, columbite-(Fe), Ilmenite, brookite, cassiterite, pyrochlore-group minerals, pyrite, arsenopyrite, and fluorite. ( Buchholz, Falster and Simmons, 2012)
MARINETTE COUNTY: Zircon is a common accessory mineral found in tiny crystals in many rocks in the county.
– Zircon forms tiny crystals included in biotite in the large quarry in the Amberg Granite near Middle Inlet in NE sec. 30 T33N R20E. (Banks and Cain, 1969).
– Zircon forms tiny crystals included in biotite in the Hoskins Lake Granite in the center of sec. 1 T37N R20 E and in the NE sec. 34 T38N R19E near Niagara (Banks and Cain, 1969).
Tiny brownish-purple zircon crystals are found with feldspars, actinolite, chlorite and biotite in a metarhyolite within the Quinnesec Formation in an outcrop on the south side of a town road in the center of sec. 25 T36N R19E (Banks and Cain, 1969).
Zircon forms tiny crystals in the Dunbar Gneiss, such as is exposed on the east side of County U in the center of the W 1/2 sec. 13 T37N R18E west of Pembine (Banks and Cain, 1969).
PORTAGE COUNTY: Zircon is an accessory in the granitic gneisses in the Linwood Quarry, NW SE sec. 8 T.23N. R.8E. These zircons give a radiometric age of 2,860 million years (Maas and Van Schmus, 1981.)
SAUK COUNTY: Tiny white, pink and yellow zircon grains are common in heavy mineral concentrates the Precambrian rhyolite, the Baraboo Quartzite and overlying Cambrian sediments near Baraboo (Becker, 1931).
WAUPACA COUNTY: Zircons are common as tiny grains scattered through the rocks of the Wolf River Batholith. Some typical localities are at the quarry in the NW NW sec. 4 T22N R12E north of Waupaca and in the SE SE sec. 26 T.25N R12E south of Big Falls along the Little Wolf River (Greenberg et. al., 1986).
– Zircon occurs in pegmatites exposed in a highway expansion on County G about 1 mile east of Big Falls (Tom Buchholz, 2002, pers. com.).