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Michigan State Gem

Michigan Chlorastrolite pebbles - click to see all state gemstones
Photo of Chlorastrolite pebbles collected in 1960 © Roger Weller: Chlorastrolite (used by permission). All Geological Symbols.

Isle Royale Greenstone (Chlorastrolite)

Michigan designated Isle Royale greenstone (chlorastrolite) as the official state gem in 1973. 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, such as on three of the stones pictured above (the pink parts are identified as thomsonite).

Polished Isle Royal greenstone - click to see all state gems
Photo of polished Isle Royale greenstone © John Jaszczak:
The Mineral Museum of Michigan - A. E. Seaman Mineral Museum (used by permission). All Geological Symbols.

Isle Royale greenstone (sometimes called green starstone or turtle back 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, cufflinks, pendants, and sometimes incorporated into inlays and mosaics.

Source:
Michigan Geological Survey: Dept. of Environmental Quality
Chlorastrolite: Central Michigan University
A. E. Seaman Mineral Museum: Mineral Museum of MI
Links:
All Geological Symbols

    

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