a black, earthy mineral consisting mainly of hydrated manganese dioxide; of importance as an ore. Being an amorphous substance, it varies considerably in chemical composition, and contains different impurities often in large amount. A variety containing much cobalt oxide is called "asbolite," while "lampadite" is a cupriferous variety. It is very soft, readily soiling the fingers, and may be considered as an earthy form of psilomelane. It results from the decomposition of other manganese minerals, and is often deposited in marshes ("bog manganese") or by springs. The name wad is of uncertain origin, and has been applied also to graphite. (L. J. S.)