isle royale greenstone

The turtleback. A mosaic of angular segments, each a slightly different green, and as you tilt it, the light moves ACROSS the segments, lighting some and skipping the one beside it. Epidote never does that.

Two names, both correct. Chlorastrolite is the one the statute uses: Act 56 of 1972 made it Michigan's state gem, effective March 1973. Pumpellyite is the mineral species it turned out to be a variety of, confirmed at the University of Michigan in the late 1940s after a century of argument over what it actually was. Rock shops and the law say chlorastrolite; a mineralogist says pumpellyite. The stone is the same either way.

Michigan's state gem. And the name is a trap: it is NOT collected on Isle Royale. The island is a national park and taking anything from it is illegal. Keweenaw beaches are where a legal one comes from.