Look out a nearby window right now. There’s a good chance you’ll see Minnesota rock.
It could be the side of a Downtown skyscraper, stone pavers, a home’s foundation, a rock wall, or just some gravel on the street. Minnesota has a lot of rock. Our geologic history is rich and there are many places to learn about it. I’ve listed a few rockhound destinations here, but to help you understand how our geologic landscape was formed, here’s a brief synopsis.
A couple billion years ago volcanoes spewed molten lava over what was to become Minnesota. The lava hardened into gray basalt seen on the North Shore and in smaller pieces nearly everywhere. Then a sea covered the area depositing different minerals. Continents collided, mountains rose, heat was generated by all the pressure and earthquakes jarred the land. The rock broke apart, melted, turned different colors from nearby minerals, swirled together with other rocks, then cooled. If the stone cooled quickly, it has an even appearance. If it cooled slower, inside the earth, it shows different colored flecks and more of a dotted texture like granite. After the rock cooled here, glaciers gouged and scraped the land exposing rock previously buried underground.
Congratulations if you made it all the way through that paragraph! You must collect rocks too.
Minnesota’s first granite quarry
In 1868, ten years after Minnesota joined the union, Breen & Young opened the first granite quarry in the state. It was located just east of St. Cloud on Highway 10. About 20 years later, the state purchased the quarry and surrounding land to build the Minnesota Correctional Facility. Inmates cut, carved and stacked the granite blocks to create the prison buildings and a 22-foot-tall, 4-foot-thick wall around the property This WPA-era monument lets visitors experience the rough strong granite blocks up close.
Quarry Park and Nature Preserve (1802 County Road 137, Waite Park)
The St. Cloud area was know as “Granite City” because of all the quarries operating in the area beginning in the late 1800s. Much of the early rock was used for curbs, bridges and building foundations, but when new polishing techniques made it possible for the hard granite to take on an attractive sheen, it became used on building facades.
Ranging from white with gray speckles to red with black streaks, granite from the area became popular on buildings of all sizes. Landmark Center and James J. Hill’s house in St. Paul both contain granite from quarries on this property.
This park’s quarrying ceased in the 1950s and it transitioned into a park and nature preserve in 1998. There are 18 quarry lakes designated for swimming, fishing and scuba diving (scuba permits are required; lakes feature unstable rock piles, cables and quarrying machinery). There are bike and walking trails, rock climbing, picnic areas, a boardwalk and quarry ruins and artifacts left throughout the park. See a mid-1900s derrick, a cutting saw, unfinished stone pillars, hoists, hooks and grout piles.
Anoka County Gem & Mineral Club
In a couple weeks, this dedicated group of rock and mineral collectors will hold their 18th-annual rock sale and swap event. Follow them on Facebook to hear about upcoming lectures, meetings or events and to see beautiful photos about recent rock discoveries. Sale and swap: 10 a.m.–2 p.m. Saturday, June 24, Osseo United Methodist Church parking lot (16 2nd Ave. SE, Osseo).
Moose Lake (about 100 miles north on Interstate 35W)
We all love Lake Superior Agates, but have you been to the Agate and Geological Interpretive Center at Moose Lake State Park? It has wonderful interpretive displays about the rocks, minerals and geology of Minnesota. The town is known as the “Agate Capital of the World,” and has the largest agate ever recorded. The giant 108-pound agate is on display at First National Bank. The third weekend of July (July 15–16, 2017) the town hosts its annual Agate Days Festival. Two dump trucks slowly drive along Elm Avenue emptying their loads of rock that are mixed with agates and quarters. Kids and adults line the streets awaiting the spill then hunt for treasures.
I never got over my rock-collecting hobby from when I was a kid. Hundreds of rocks were stashed in my closet in old coffee cans. When I found out about Minnesota quarries I started collecting slabs.
Granite showrooms are filled with slices of stone in all sorts of colors and textures from Minnesota and around the world. Tables and counters in my homes have included two colors of St. Cloud granite, Mesabi Black granite, Morton Gneiss, Kasota limestone from Mankato, travertine from Winona and Sioux Quartzite from a quarry near Pipestone. I’m very lucky to have a metal worker for a friend — she makes a lot of table bases for me.
Summer is a great time for seasoned and emerging rockhounds. And in case you didn’t know, Lake Superior agates can be found throughout the Twin Cities area. When you walk toward the sun, look for the light to shine through them. Happy hunting!
Next issue: Twin Cities buildings featuring rock from Minnesota quarries
Just for fun, have lunch at Rosedale’s Granite City Food & Brewery, a St. Cloud restaurant chain that opened 1999 and has 36 restaurants in 14 states.
- Lake Superior Agates formed inside air pockets in the rocks and were dislodged by glaciers and other kinds of weathering.
- Ely Greenstone is one of the oldest rocks in the world. Look for parallel streaks on the surface that show where glaciers pushed across the rock.
- Rocks with rings around them were broken up during earthquakes. Minerals filled in all the cracks then the rock broke into smaller pieces again and were worn smooth and round.