This is a mixture of silver sheen, some rainbow, and some jet black, all from California's famous Davis Creek area. Obsidian is volcanic glass, and is the sharpest material known--it is still used for surgeon's scalpels. You can cut this material for cabochons or break it for tumbling--all those sharp edges will quickly disappear, because it is so soft (Mohs 5.5). The trick is to start a batch with 50% Ceramic Shape Mix and then grind out the imperfections & spalled areas after two weeks in Stage 1. Then take your time with the remaining stages and watch it shine up like crazy. Figure to break it to quarter size or slightly larger for a jewelry mix. This is 5 Lbs of Black Obsidian in a bag at $4.50/Lb.