Chlorastrolite pebbles collected in 1960; photo © Roger Weller / Central Michigan University (all rights reserved; used by permission).
Official State Gem of Michigan
Michigan designated Isle Royale greenstone (chlorastrolite) as the official state gem in 1973. All State Gems
Chlorastrolite (a variety of the mineral pumpellyite) is a bluish-green stone with a pattern of slender, star-like crystals which results in a "turtle back" pattern. Some chlorastrolite includes other minerals, which produce additional colors.
Isle Royale greenstone (sometimes called "green starstone" or "turtleback" in Michigan) is usually found as bean-sized, rounded beach pebbles (collecting chlorastrolite from Isle Royale National Park is now prohibited). Polished stones are used for stickpins, rings, earrings, cuff links, pendants, and sometimes incorporated into inlays and mosaics.