Minnesota is a good state for rockhounding. Minnesota is famous for ‘Lake Superior Agates’ (as well as its enormous iron deposits). In fact, Moose Lake, Minnesota has dubbed itself the ‘agate capital of the world’ and Agate Days is celebrated there each year in July. Minnesota, however, has lots of rockhounding opportunities beyond Lake Superior Agates. Although many people are aware that Minnesota was impacted by the most recent Ice Age, non-rockhounders often are unaware of Minnesota’s volcanic past or that vast seas once covered it. This geologic history, however, is important and, as a result, Minnesota has a variety of igneous, sedimentary, and metamorphic rocks.
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 Gemstone: Lake Superior Agates (1969)
Minnesota designated Lake Superior agate as its official state gemstone in 1969. Interestingly, the statute subsequently was amended to require that a photograph and a typical specimen of the Lake Superior agate be preserved in the Office of the Secretary of State. Lake Superior agates (sometimes called 'lakers') are noted for their red, orange, and yellow coloring (the agates also include white and grey coloring) that is due to iron. The history of Lake Superior agates traces back to about a billion years ago. The North American continent began to split, creating a large rift valley, and lava welled up in the area of what is now Lake Superior. Bubbles of air were trapped in the lava. After the lava cooled, water seeped into the holes created by the bubbles and deposited iron, quartz, and other minerals in layers, creating agates. As the surrounding volcanic rock was worn away by erosion or the scouring action of glaciers, agates were released from the lava and moved to other places. In Minnesota, these agates are found in the northeastern and north central part of the state. Lake Superior beachcombers often can find these agates. Most of the agates are small, but large specimens can weigh over twenty pounds.
State-specific rockhounding books (including the books listed here as well as other books), regional rockhounding site guides, and other helpful rockhounding resources are identified - by category - in the Books & Gear section of Gator Girl Rocks with a link to the Gator Girl Rocks Amazon Store where you may easily browse selected resources and securely place an order. Your order will benefit Charity Rocks!
Minnesota Geological Survey
The Minnesota Geological Survey has one of the nation’s better websites and provides a wealth of information regarding Minnesota geology. The site includes a ‘virtual egg carton’ with rocks displayed there. My dad got a kick out of that as, when he was a small boy, he kept his special rocks in a rock carton. He’s so ‘old school’ but he is my best rockhounding pal.
Minnesota Department of Natural Resources
The website section regarding Minnesota Minerals is useful.
- Richard W. Ojakangas, Roadside Geology of Minnesota (2009).
- Bob Lynch & Dan Lynch, Lake Superior Rocks & Minerals: A Field Guide to the Lake Superior Area (2008).
- Mark Sparky Stensaas & Rick Kollath, Rock Picker’s Guide to Lake Superior’s North Shore (2d ed. 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. 3 - Northwestern Quadrant (1986; 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
Science Museum of Minnesota
Saint Paul, Minnesota
The Science Museum's Triceratops, one of only four real mounted Triceratops specimens in the world, is also the largest complete Triceratops specimen on display.
Agate and Geological Interpretive Center
Moose Lake State Park
The Agate and Geological Interpretive Center at Moose Lake State Park exhibits Lake Superior agates.
Minnesota Museum of Mining
The Minnesota Museum of Mining focuses on the history of the iron mining industry in Minnesota. At one time there were more than 100 mining pit operations in or near Chisholm, which is located in the heart of northern Minnesota's Mesabi Iron Range. The Mesabi, Vermilion, & Cuyuna iron ranges make up the largest concentration of iron ore in the world.
Places to Visit - Interesting Sites To See
Pipestone National Monument
Southwest Minnesota north or Pipestone, Minnesota
Indian tribes quarried catlinite (a brownish-red mudstone) at this site to make ceremonial pipes.
Mystery Cave State Park
Visitors can take a cave tour and see stalactites (calcite deposits hanging from the cave roof) and stalagmites (calcite deposits rising from the cave floor). Visitors also can see standing pools and flowstone that formed when groundwater saturated with calcium carbonate evaporated within a rock cavity. The entrance to Minnesota’s longest-known cavern is five miles west of the main park. Thirteen miles of winding passage were carved into the limestone bedrock over many thousands of years, and the South Branch Root River still feeds this living cave before flowing through the park proper.
Soudan Underground Mine State Park
Visitors can go almost a half-mile below the surface to view the world of underground mining. Opened in 1883, the Soudan Mine is Minnesota's oldest and deepest iron ore mine. Ely Greenstone, volcanic rocks, and sediments formed in oceans over 2.7 billion years old, may be seen here.
Hill Annex Mine State Park
This park is an old open pit iron ore mine. Visitors can see the Coleraine Formation, a layer of material composed of shale, sandstone, and iron ore conglomerates. This formation was created 105 to 60 million years ago when an ancient sea covered the Mesabi Range area. The formation is a good source of fossilized shark's teeth, ocean snails, clams, and crocodile parts. Fossil hunting tours are available by reservation through the Hill Annex State Park.
Rockhounding Sites for Children & Families
Despite their name, Lake Superior agates can be found throughout much of Minnesota. That's because 10,000 years ago, glaciers carried them far from their origin in the Lake Superior region. People often look for them on the banks or at the mouths of rivers, in gravel pits, or in other places where pebbles and gravel abound.
Lilydale Regional Park – Saint Paul, Minnesota
Recreational fossil collecting is allowed at this park. The fossils are exposed because of prior excavation pertaining to a brickyard operation. A wide variety of fossils occur at this site.
Fossils – Algae
Fossils may be found throughout the state of Minnesota, but are more common in certain areas. The oldest fossils in the state are found in the Precambrian iron formations in northeastern Minnesota. These primitive algae fossils are over two billion years old! They were one-celled organisms that lived in the shallow seas that covered much of Minnesota.
Fossils – Snails, Clams,
Oysters, & Shark Teeth
North Central Minnesota
During the Devonian Period (380 million years ago) southern Minnesota was covered by a sea, leaving fossils of fish and corals scattered throughout the area. Fossil snails, clams, oysters and shark teeth can be found in north central Minnesota dating to 100 million years ago (the Cretaceous Period).
Fossils – Trilobites
Trilobites and cephalopods can be found in southeastern Minnesota, which was covered by a shallow sea that reached up from the Gulf of Mexico during the Ordovician Period, 440 million years ago.
Moose Lake, Minnesota
Moose Lake hosts an ‘Agate Days Celebration’ (usually the third Saturday in July). Along with a rock and gem show, the town has dumped gravel on Main Street and, mixed in with the gravel, are agates.