[1] Chlorastrolite has finely radiating or stellate (for examples, see crystal habits) masses that have a "turtleback" pattern.
Chlorastrolite occurs as amygdaloid structures and fracture fillings in basalt, and when the water and wave action has worn away the basalt, they are found as beach pebbles and granules in loose sediments.
Isle Royale is a National Park, and so it is illegal to collect specimens there.
Most gem quality chlorastrolite stones are very small, and it is rare to find one that is larger than a half inch.
The largest gem quality stone is in the Smithsonian Museum and measures 1.5 by 3 inches.