Isle Royale greenstone, this state's official gem, is found on Isle Royale in Lake Superior
They are only found in 
the Keweenaw Peninsula and on Isle Royale (harvesting ... Lake Superior 
Agates, Datolite, Prehnite, Thomsonite, and many other minerals from... [DOC] [TLE] Isle Royale Greenstone State Gem | State Symbols USA [PAR] Michigan designated Isle Royale greenstone (chlorastrolite) as the official ... 
found as bean-sized, rounded beach pebbles (collecting chlorastrolite from Isle... [DOC] [TLE] Da Yooper's Rockhound and Lapidary Guide to Isle Royale ... [PAR] Isle Royale Greenstone, ( Chlorastrolite ) a variety of Pumpellyite, Ca2(Al,Mg ... 
named after Isle Royale, the island in Lake Superior on which they can be found.