Gator Girl Rocks

Rockhounding Wisconsin

Wisconsin is a good state for rockhounding.  The state is noted for its enormous iron ore deposits.  Gemstones are found quite commonly in Wisconsin – the Lake Superior Agate is found in every county.  Collectors also may find a diamond - especially in the counties around Milwaukee.  The diamonds are the result of glacial activity and the source of the diamonds is unknown.  In addition, there are abundant marine fossils in Eastern and Southern Wisconsin.  Wisconsin also has numerous glacial features throughout the state from the last ice age glaciers, including kettles (bowl-shaped depressions), eskers (snake-like ridges), and drumlins (elongated, rounded hills).  Wisconsin (like many other states) also has meteorite strewnfields such as the 2010 Mifflin meteorite in Iowa County, Wisconsin.

 

State Rocks, Gemstones, Minerals, Fossils, & Dinosaurs

Rockhounding Tip:  Knowing state rocks, gemstones, minerals, fossils, and dinosaurs often can be very useful information for rockhounders.  Ordinarily, states with significant mineral deposits, valuable gemstones, fossils, or unusual or significant rock occurrences will designate an official state mineral, rock/stone, gemstone, fossil, or dinosaur to promote interest in the state’s natural resources, history, tourism, etc.  Accordingly, such state symbols often are a valuable clue as to potential worthwhile rockhounding opportunities.

State Rock:  Red Granite (1971)
Wisconsin designated red granite as its official state rock in 1971.  Granite is an intrusive igneous rock made up of a variety of minerals – typically quartz, feldspar, mica, and hornblende.  Granite commonly is used as a building and decorative stone.  Red Granite is mined in several sections of the state.

 

State Mineral:  Galena (1971)
Wisconsin designated galena as its official state mineral in 1971.  Galena is the most important mineral source of lead.   It crystallizes as dark gray/silver cubes and is heavy (specific gravity 7.5+). 
 Galena is formed in a wide range of hydrothermal environments.  It is extremely abundant in the low temperature hydrothermal deposits widely known as Mississippi Valley type deposits such as is found in the southwestern part of the state.  The deposits in the southwestern part of Wisconsin (primarily in Grant, Iowa, and Lafayette Counties) are internationally known as a major part of Upper Mississippi Valley zinc-lead district. This district extends into adjacent Iowa, and Illinois. 
 Galena has been produced from the Upper Mississippi Valley zinc-lead district in Wisconsin since the seventeenth century.  Some mines started by Native Americans may predate this.  Major lead mining occurred from the 1800's until the late 1970's.  A few small lead mines operated by individuals persist to the present day.  Others are presently preserved for tourists.  Hundreds of mines of all sizes are known from the district.  Many were small shallow diggings. The Wisconsin state mascot, the badger, is a reference to the miners and their numerous "badger holes."
 Most of the mines in the district are now inaccessible, either being overgrown, collapsed, filled-in or leveled.  Most of the dumps have been removed for road material.  Still, piles of waste rock, featuring some interesting mineral collecting persist in the area as testimony to the extent of the mining. 
 The galena in the Upper Mississippi zinc-lead district often occurs in coarse masses in veins up to three feet thick and several yards long.  Coarse crystals ("cog ore") are also common and are dominated by cube and octahedron.

State Fossil:  Calymene celebra (1986)
Wisconsin designated Calymene celebra, a trilobite, as its official state fossil in 1986.  This trilobite inhabited the reefs that flourished in the shallow seas that covered the state during the Late Ordovician and Silurian Periods, some 460 - 400 million years ago.  At that time, Wisconsin was about 30 degrees south of the equator, and the coral reefs that were abundant in the warm seas were home to a teeming ecosystem of brachiopods, mollusks, and crinoids, as well as trilobites.  Trilobites were arthropods (related to insects and crabs), and as such, possessed a segmented body, jointed appendages, and an exoskeleton.  Calymene was a bottom-dweller that crept along the sea floor in search of food.  Calymene itself lasted only until the end of the Devonian, and all trilobites went extinct at the end of the Paleozoic Era in the mass extinction that wiped out nearly all of the species on earth.  
Calymene specimens are frequently found in limestones and dolomites in the southern part of the state, because glacial action has obscured fossil-bearing outcrops further north.

 

Rockhounding Resources

Wisconsin Geological & Natural History Survey

 

• Robert H. Dott, Jr. & John W. Attig, Roadside Geology of Wisconsin (2004).
• Bob Lynch & Dan Lynch, Lake Superior Rocks & Minerals:A Field Guide to the lake Superior Area (2008). 
• June Culp Zeitner, Midwest Gem, Fossil, & Mineral Trails: Great Lakes States (Rev. ed., June 1999 - first published in 1955).
• June Culp Zeitner, Midwest Gem Trails: Field Guide for the Gem Hunter, the Mineral Collector, and the Tourist (3d. Rev. ed., 1964 - originally published in 1956).
• Allan W. Eckert, Earth Treasures Vol. 1 - Northeastern Quadrant (1985; reprint in 2000).
• James Martin Monaco & Jeannette Hathway Monaco, Fee Mining & Mineral Adventures in the Eastern U.S. (2d ed., 2010).
• Kathy J. Rygle & Stephen F. Pedersen, Northwest Treasure Hunter's Gem & Mineral Guide (4th ed. 2008).

 

Museums of Interest to Rockhounders

Geology Museum
University of Wisconsin Madison – Madison, Wisconsin
The museum has an extensive collection and exhibits of rocks, minerals, and fossils.  In addition, the museum exhibits Wisconsin meteorites.

 

Weis Earth Sciences Museum
University of Wisconsin Fox Valley – Menasha, Wisconsin
The Weis Earth Sciences Museum is the official mineralogical museum of Wisconsin.  The museum’s exhibits include a lead mine, a dinosaur den, and rocks, minerals, and fossils.

 

Mining Museum
Platteville, Wisconsin
The museum focuses on lead and zinc mining.

 

Milwaukee Public Museum
Milwaukee, Wisconsin
The museum displays the Hebior Mammoth, which was found just 30 miles from the museum.  In addition, the museum’s Third Planet Hall focuses on plate tectonics.

 

Museum of Natural History
University of Wisconsin-Stevens Point – Stevens Point, Wisconsin
Museum includes rock, mineral, and fossil displays.

 

Museum of Minerals & Crystals
Dodgeville, Wisconsin
The museum displays rocks, minerals, crystals, and fluorescents.

 

Iron County Historical Society Museum
Hurley, Wisconsin
The museum includes exhibits pertaining to local mining.

 

Places to Visit - Interesting Sites To See

Quarry Lake Park
Racine, Wisconsin
Silurian reef fossil deposits are exposed at quarry Lake Park.  This former quarry (now a pool) is in the Racine Formation. 

 

Cave of the Mounds
Blue Mounds, Wisconsin
Cave of the Mounds is a limestone cave with a wide variety of speleothems including stalactites, stalagmites, soda straws, flowstones, curtains, helictites and oolites.

 

Crystal Cave
Spring Valley, Wisconsin
Crystal cave is formed in dolomite.  Stalactites, stalagmites, and rippling flowstone can be seen hanging from the ceiling or covering the ledges of the cave.

 

Rockhounding Sites for Children & Families

Lake Superior Agates
Lake Superior Shoreline
A billion years ago, a 1,20-mile rift formed in the middle of what is now the United States.  It continued to deepen and widen for perhaps 20 million years.  When it stopped, lava poured out, creating vast basaltic deposits and leaving the long basin that is now Lake Superior.  Some components of the molten basalt escaped as gas, leaving pockets.  Over millennia, agates formed in these pockets. Today, beachcombers on Wisconsin’s Lake Superior shoreline often find these souvenirs of midwestern geological formation.

 

Meteorites
Iowa County, Wisconsin
The 2010 Mifflin Meteorite attracted significant attention.