After her recent visit to Traverse City, Michigan, my daughter Marie gifted me with some Petoskey stones. I’ve always loved these beautiful stones, especially when polished and set into jewelry. This week, we’ll hunt for them as we travel to the Lower Peninsula of Michigan. Then we’ll hop to the Upper Peninsula and beyond to search for famous Lake Superior agates.
Sharon Lyon
Editor, GeoLifestyle
Petoskey Stones
My Petoskey stone collection - unpolished (left), polished (middle). and set into jewelry.
Petoskey stones are both rocks and fossils, composed of the fossilized colonial rugose coral Hexagonaria percarinata.
When dry, the stone looks like ordinary limestone, but when wet or polished, it reveals its distinctive hexagonal coral pattern, sometimes called the “rays of the rising sun.”
Petoskey stones are usually light to dark grey in color, but rarely, they can contain iron, which gives them a pink hue. The pink ones are known as “Pink Pets.”
The stone and the city of Petoskey were named for the 19th-century Ottawa (Odawa) Chief Petosegay, his name translating to “rays of dawn” or “rising sun.”
Petoskey stones were named Michigan’s state stone in 1965.
Geology: Petoskey stones are found in the middle Devonian (350-million-year-old) Gravel Point Formation, part of the Traverse Group. The Gravel Point is primarily a fine-grained limestone, with shale beds, chert nodules, and reef-like masses of corals and stromatoporoids.
The limestone was deposited in the warm, shallow sea when Michigan was located near the equator. The coral thrived in the tropical, low-energy reef on a marine shelf in the Michigan Basin.
Glacial action about two million years ago plucked, smoothed, and scattered the fossilized coral fragments across Michigan’s northern Lower Peninsula.
Where and when to find them: Petoskey stones can be found along Lake Michigan beaches from Traverse City to Petoskey, especially around Little Traverse Bay.
The best time to hunt is in the Spring, after the lakes’ ice has churned and exposed new stones; good hunting continues through late Fall.
Popular hunting beaches: Petoskey State Park has one mile of beach between Petoskey and Harbor Springs that is known for excellent Petoskey Stone hunting.
Magnus Park City Beach has 1,000 feet of shoreline within walking distance of downtown Petoskey and is accessible and convenient.
Solanus Mission Beach hosts 500 feet of accessible beach, with a boardwalk and overlook on Little Traverse Bay. This beach is sacred to the Odawa, so visitors are asked to be respectful.
Inland sites: Glaciers also spread fossils inland, so the stones can be found in gravel pits and roadcuts.
Hunting tip: Wet the stones to reveal their hexagonal pattern—carry a water bottle to spray them when searching away from water.
Bonus scenery: The drive from Traverse City to Petoskey is picturesque, with scenic towns along Lake Michigan.
Be sure to tour the eclectic Mushroom Houses of Charlevoix. Designed and built by Earl Young in the early 20th century to accommodate the landscape, the houses’ walls are composed of limestone, fieldstone, and other boulders from local sources.
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The Lake Superior Agate is Minnesota’s state gemstone and is known for its rich red, orange, tan, and yellow bands. The agates can be found in Canada and in the United States in states surrounding Lake Superior.
What are agates? Agates are a type of microcrystalline quartz (chalcedony) that are banded in concentric rings or irregular patterns.
Agates are somewhat translucent, meaning that light can pass through the stone.
They have a glassy or waxy sheen when polished or wet.
Geology: 1.1 billion years ago, during the creation of the Midcontinent Rift System (Keweenawan Rift), vast basaltic lava flows covered the region. The flows trapped gas bubbles, forming vesicles (cavities) in the basalt.
Later, groundwater rich in silica, iron, and copper filled the vesicles. Layers of minerals were deposited sequentially, forming the banded chalcedony and quartz. Iron oxides produced the characteristic red and orange hues.
During the Ice Age, glaciers eroded and transported agates, scattering them across Michigan, Minnesota, Wisconsin, and beyond.
The Upper Peninsula of Michigan is exceptionally rich in agates. Try your luck at these beaches:
Grand Marais/Agate Beach features an excellent rock-hunting area at the start of Pictured Rocks National Lakeshore. (You must stay outside the park boundaries to collect).
Crisp Point is known for its agate-rich shorelines near the historic lighthouse.
Little Girls Point, near Ironwood, is a popular agate-hunting beach. You can kayak to nearby Superior Falls and Superior Cliffs.
Manitou Island is a small island off the northeast tip of the Keweenaw Peninsula, with productive shoreline spots.
In Minnesota:
Visit Beaver Bay and hunt for agates at the mouth of the Beaver River.
Gooseberry Falls State Park features an agate beach with a changing shoreline and new discoveries after storms.
Along the North Shore of Lake Superior, from Duluth to Grand Marais, there is prime hunting after storms or heavy winds.
In Wisconsin:
Check out the beach at Chequamegon Point in Ashland.
Hunting tips: Look for rocky beaches and explore in knee-deep water.
The water is cold! 🥶Wear rubber boots and bring a bucket.
Search for shiny, waxy surfaces and translucent glows when light hits the stone. Look for beige, red, maroon, and white, with visible banding or unique patterns.
Polishing: Use a rock tumbler for a smooth, glossy finish.
Learn more about agate hunting via this video with the owners of Beaver Bay Rock Shop here.
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