Totally bounded by faces, this translucent and partially hollow specimen, occurs as the non crystalline center of certain agates. Definitely not a common occurrence in the stock of mineral dealers. I have never seen one of these from anywhere but Brazil. From California ?!?! NOTE FROM A FRIEND: These polyhedrons occurred in a Tungsten mine near Bishop, California. The correct spelling is "Pine Crik," according to Ed Weber (Weber's Minerals of Encinitas). I got mine from Ed, who had them in his geode collection. According to Ed; these were found in the late 60's through the early 70's. - Russ Rizzo