Stories We Like: A Guide to the Comma
black and earthy substance that consists mainly of hydrated manganese oxides; it is an important ore of manganese. It varies considerably in chemical composition and contains different impurities, often in large amounts. Wad is very soft, readily soils the fingers, and may be considered to be a mixture chiefly of pyrolusite and romanechite. It results from the decomposition of other manganese minerals and is often deposited in marshes or by springs; it bears the same relationship to manganese oxides that limonite and gummite do to iron and uranium oxides.