Where: Michigan · North America · approx. 47.47, -87.88 (vicinity only)
Why this spot: Precambrian basalt amygdules
What turns up: Chlorastrolite (greenstone) pebbles, the Michigan state gem, in shoreline gravel
Access: Open / legal.
Collect small greenstones on mainland public beaches; collecting is prohibited inside Isle Royale National Park.
Open in Mudlark Map →
Satellite view, historic-map overlays, tide/flow context and field notes are in the app. Exact research detail is part of Pro.
Pins are approximate by design. This page is historical research, not permission to dig. Check ownership and local law first.