Cook County, Minnesota is the perfect place to look for the Minnesota state gem: the Lake Superior agate. Here are four things to know that will help you find some gems of your own. After you’ve perused the tips, read more about our Way North of Ordinary geology.
How to find Lake Superior agates
• Know where to look.
Hunt for agates on any public beach or other location that has exposed rock gravel. Also keep your eyes peeled when walking gravel roads. Some locations allow only looking, not taking, so check before you pocket that agate.
• Know what to look for.
It’s not always obvious a rock is an agate. Wet it and look closely for translucency, banding and a glossy, waxy sheen.
Like people, agates come in many forms and colors. If you are lucky, you might find a rare “eye” agate with two sets of ring bands. “Fortification” agates have colored bands, completely connected, circling the face of the agate. Parallel-banded fortification agates are sometimes called “water-level” agates and have straight parallel bands running across the face.
• Dig deeper.
When agate-hunting on the beach, dig down several inches to where the rocks are wet. Because agates are semi-translucent, they glisten when wet.
Remember that you’re not looking for large rocks. Most agates are between the size of an almond and a walnut.
• Think outside the beach.
Agates can be found anywhere rocks have be dropped by glaciers, or moved by humans. While Lake Superior’s shoreline may be the most picturesque place to find agates, you’ll find them in gravel pits and on dirt roads, too.
How did Lake Superior agates form?
Every Lake Superior agate was born a billion years ago, when a massive lava flow solidified and formed the bed of Lake Superior. Bubbles in the lava were preserved as pockets.
Over time, mineral-rich water seeped into those bubbles (called vesicles), forming layers. The color of the layer depends upon the mineral content of the water. During the last Ice Age, glaciers scraped the agates out of the hardened lava and scattered them along the North Shore.
These tips come from Mandy T., an agate fiend who works at the Grand Marais Visitor Information Center.
Additional information came from The Lake Superior Agate by Scott F. Wolter and Rock Picker’s Guide to Lake Superior’s North Shore by Mark Stensaas, illustrated by Rick Kollath.