It's a beautiful stone that according my new gem book, Gemstones of the World, by Walter Schumann, is an ore of tin. The primary colors are gray and brown, but it can have white, yellow and red.
This particular strand of beads has some really nice reddish-brown streaks. That's why I chose to use some glossy carnelian rounds as accent beads.
These unique earrings are for sale in my etsy shop.