Nephrite

Nephrite is a variety of Actinolite/Tremolite made up of tough, hard, interwoven fibers. Nephrite is one of the two minerals that make up Jade. The other is Jadeite.

The most extensive American Nephrite deposit is in the middle portion of southern Wyoming. This deposit is enormous, yielding tons of this ornamental stone. Alaska also contains several large deposits, namely in the Jade Mountains (also known as the Cosmos Hills) and in Jade Creek. Large deposits are also in the Shungnak River and the Dahl Creek.
An enormous, underwater deposit, known as "Jade Cove" exists off the California coast in Monterey Co, California, near the coast by Plaskett Point. Rounded pebbles are also found in the nearby beach area, (called "Jade Beach").