Rock Hounding the Keweenaw: Agates, Native Copper, and Greenstone

Lake Superior agates are the prize everyone knows — but the Keweenaw offers more than most people realize. Native copper, Keweenaw greenstone (chlorastrolite), and a range of secondary copper minerals wash out of the basalt along the shore. You won't find this combination many other places in the world.

Lake Superior Agates

Formed about 1.1 billion years ago during volcanic activity that also deposited the Keweenaw's copper, Lake Superior agates are distinguished by their iron-red and orange banding. They're heavy for their size and catch light differently than plain quartz. The best time to find them is after a storm has turned the gravel, or early morning before anyone else has walked the beach.

Native Copper

The Keweenaw is the only place in the world where native copper — pure metallic copper not chemically combined with other minerals — occurred in minable quantities. The mining ended, but the copper didn't go anywhere. Pieces wash out of the basalt constantly. Green oxidation (malachite) on a rock is your first clue. Heavier than expected for its size is the other tell.

Keweenaw Greenstone

Chlorastrolite, the Michigan state gem, is found almost exclusively on the Keweenaw and Isle Royale. Tiny — rarely larger than a thumbnail — and green with a turtleback pattern when polished. It's the rarest of the three and takes patience to find. It occurs in the amygdules (gas pockets) in the basalt, and sometimes washes loose onto the beach gravel.

Where and When

The best gravel beaches are not the ones with parking lots. Storms and wave action sort the gravel and bring new material up from depth — the best hounding is always after rough water, not during the glassy calm. Our guided rock hounding sessions take you to spots we've spent years scouting, with the knowledge of what to look for and where the gravel has been working.