AD-99.5% Alumina Mortars and Pestles are recommended for precise elemental analysis because they provide minimal sample contamination. AD-99.5% Alumina is an extremely hard (9 on Mohs scale), non-absorbent, wear-resistant material. Octagon-Style Mortar: Glazed completely except inside grinding surface. Pestle: Glazed completely except grinding surface. M = Mortar P = Pestle.