Spiny oyster is not a stone! It's a marine shell from the spiny oyster (Spondylus species - I had to look that up). The shell is naturally dense and vividly colored, producing shades of orange, red, purple, white, and sometimes yellow. Because it’s solid and takes a high polish, it has been used in jewelry for thousands of years. Today, we buy in compressed blocks at the Tucson Gem and Mineral Show, which Ben can cut into slabs and work into cabochons. We also have pieces from Ed Lohman and First American Traders!