Mahogany obsidian slabs are 3/8" thick and are irregular shaped slabs which will be great for flintknappers for knives, etc. The reddish brown (pumpkin color) and black slabs of obsidian were slabbed from a large boulder and slab sizes will vary.  Send an e-mail if interested and in what lengths of slabbed obsidian will suit your purpose, such as 5" up to 8" plus lengths. One slab may vary from 1 order (containing 5 square inches or 2 1/2" x 2 1/2") up to possibly 5 orders in one slab and therefore a number of knife blades can be made from one slab. Stock number 548-3-8s.