Sapphire Mortar and Pestle Made of finely powdered synthetic sapphire and a specially processed form of pure aluminum oxide. Inert to most corrosive chemicals. Volume: 111ml. Height: 50mm. Depth: 38mm. 122mm OD. 100mm ID. Pestle: 100mm. Specific gravity: 3.6. Hardness: approximately 9 on Mohs scale.