Chlorastrolite

Chlorastrolite, also known as Isle Royale Greenstone, is a green or bluish green stone.[1] Chlorastrolite has finely radiating or stellate (for examples, see crystal habits) masses that have a "turtleback" pattern. The stellate masses tend to be chatoyant, meaning they have a varying luster. This chatoyancy can be subtranslucent to opaque. Cholorastrolite is a variety of pumpellyite: Ca
2(Mg,Fe)Al
2(SiO
4)(Si
2O
7)•(OH)
2H
2O. Chlorastrolite was once thought to be an impure variety of prehnite or thomsonite.

  1. ^ Arguably the rarest gemstone in the world and one of the most valuable American gemstones. The gem quality specimens are typically found on Isle Royale, a large island off the Northeastern tip of Minnesota. a Michigan's State Gemstone