A 60/80 mesh manganese dioxide ore. Added to a stoneware clay body, it creates large, dark, reactive, reduction-like specking. The effect is enhanced with powdered manganese dioxide. In glazes it creates dark brown, reactive speckles although uniform results are problematic due to settling in glaze containers. Above 1080º C MnO2 changes to MnO, an active flux; glazes that are molten at 1080º C may show defects due to liberated O2.