Portsmouth Mine: Agate & Chalcedony Rockhounding in Crow Wing County, Minnesota

Updated June 2026

Portsmouth Mine is a mapped rockhounding spot in Crow Wing County, Minnesota. Reported finds include agate, chalcedony, jasper, binghamite, manganese, and more. Below: coordinates, access notes, nearby spots, and trip-planning links.

Quick details

Access: Public area
County: Crow Wing County
State: Minnesota
Nearest road: Portsmouth Campground Trail
Postcode: 56441
Coordinates: 46.49079, -93.97144

Geology at Portsmouth Mine

This spot sits on Iron-formation in the Cuyuna North and South Ranges and Mille Lacs Group, mapped as banded iron formation that formed roughly 2500 to 1600 million years ago. Tough silica like agate and jasper typically survives weathering and collects as float in drainages and gravel.

Mapped unit: Iron-formation in the Cuyuna North and South Ranges and Mille Lacs Group
Age: 2500–1600 Ma (Paleoproterozoic)
Rock types: banded iron formation
Elevation: 1,230 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 Portsmouth Mine

Best months: April to October. Typical highs run 81°F in midsummer and 21°F in midwinter, with winter lows near 0°F.

Climate normals: NOAA 1991-2020 monthlies, BRAINERD CROW WING CO AP station (10 mi away).

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 Portsmouth Mine

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 Portsmouth Mine.

Portsmouth Mine FAQ

Where is Portsmouth Mine?+

Portsmouth Mine is in Crow Wing County, Minnesota, at 46.49079, -93.97144. Nearest road: Portsmouth Campground Trail.

What rocks and minerals can you find at Portsmouth Mine?+

Portsmouth Mine is reported to produce Agate, Chalcedony, Jasper, Binghamite, Manganese, Iron.

Is collecting allowed at Portsmouth Mine?+

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 Portsmouth Mine?+

Most agate and jasper is surface float: bring a spray bottle, a pick or small shovel, and a sturdy bag. Wet stones show their banding and translucence.

When is the best time to visit Portsmouth Mine?+

The most comfortable months at Portsmouth Mine are April to October.

How do I get to Portsmouth Mine?+

Open the directions link to navigate to 46.49079, -93.97144 in Google Maps. The nearest road is Portsmouth Campground Trail.

More rockhounding in Minnesota

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Open Portsmouth Mine on the map

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