Chlorastrolite

Chlorastrolite also known as Isle Royale Greenstone, is a green or bluish green stone. Chlorastrolite has finely radiated or stellate masses that have a "turtleback" pattern. The stellate masses tend to be chatoyant, meaning they have a changeable luster. This chatoyancy can be subtranslucent to opaque. Cholorastrolite is a variety of pumpellyite: Ca₂(Mg,Fe)Al₂(SiO₄)(Si₂O₇)(OH)₂·H₂O. Chlorastrolite was once thought to be an impure variety of prehnite or thomsonite.