Thomsonite Beach: Chlorastrolite & Lintonite Rockhounding in Cook County, Minnesota

Updated June 2026

Thomsonite Beach is a mapped rockhounding spot in Cook County, Minnesota. Reported finds include chlorastrolite, lintonite, thomsonite nodules. Below: coordinates, access notes, nearby spots, and trip-planning links.

Quick details

Access: Public area
County: Cook County
State: Minnesota
Nearest road: MN 61
Coordinates: 47.72778, -90.45836

Geology at Thomsonite Beach

This spot sits on Basalt and basaltic andesite, mapped as basalt and basaltic andesite that formed roughly 1200 to 1000 million years ago. Volcanic ground like this weathers into rocky slopes and float, and fresh exposures in cuts and drainages are usually the most productive places to look.

Mapped unit: Basalt and basaltic andesite
Age: 1200–1000 Ma (Mesoproterozoic)
Rock types: basalt and basaltic andesite
Elevation: 910 ft

Geologic mapping via Macrostrat and the underlying state geological survey maps (CC BY 4.0). Bedrock at the surface can vary within a mapped unit.

Best time to visit Thomsonite Beach

Best months: May to October. Typical highs run 69°F in midsummer and 23°F in midwinter, with winter lows near 6°F.

Climate normals: NOAA 1991-2020 monthlies, GRAND MARAIS station (5 mi away), adjusted for elevation.

Land & collecting status

Generally open to casual rockhounding

Most public-tagged spots sit on BLM, U.S. Forest Service, or other federal land where reasonable hand collecting of common rocks and minerals is allowed. Confirm posted rules and active mining claims before you dig.

Public-land rules vary by agency, season, and field office. The RockHoundR app pulls live BLM, USFS, NPS, and tribal overlays so you can see exactly which agency manages the ground at this spot.

Sources & verification

Spot details combine the public RockHoundR location dataset, normalized mineral labels, agency land-status checks in the app, and community submissions. Coordinates are approximate until verified in the field.

Sources: RockHoundR public spot dataset, app land overlays, and local agency review before each trip.

Found at Thomsonite Beach

Each chip opens all spots that produce that material; the encyclopedia link opens the full ID and field guide.

Nearby rockhounding spots

Other rockhounding spots within driving distance of Thomsonite Beach.

Across the state line from Thomsonite Beach

Thomsonite Beach is close enough to the Minnesota border that the next-closest rockhounding spots are in a neighboring state. Worth knowing if you are already on the road.

Thomsonite Beach FAQ

Where is Thomsonite Beach?+

Thomsonite Beach is in Cook County, Minnesota, at 47.72778, -90.45836. Nearest road: MN 61.

What rocks and minerals can you find at Thomsonite Beach?+

Thomsonite Beach is reported to produce Chlorastrolite, Lintonite, Thomsonite Nodules.

Is collecting allowed at Thomsonite Beach?+

Generally open to casual rockhounding. Most public-tagged spots sit on BLM, U.S. Forest Service, or other federal land where reasonable hand collecting of common rocks and minerals is allowed. Confirm posted rules and active mining claims before you dig. Always confirm current rules with the managing agency before a trip.

What tools should I bring to Thomsonite Beach?+

A rock hammer, sturdy gloves, safety glasses, and a collecting bag cover the basics here. Add a spray bottle: wet rock shows color and pattern that dry rock hides.

When is the best time to visit Thomsonite Beach?+

The most comfortable months at Thomsonite Beach are May to October.

How do I get to Thomsonite Beach?+

Open the directions link to navigate to 47.72778, -90.45836 in Google Maps. The nearest road is MN 61.

More rockhounding in Minnesota

See all 49 Minnesota spots →

Open Thomsonite Beach on the map

Use the RockHoundR app for live land overlays, weather, geology, directions, and saved finds.