- Black iron oxide - An oxide of iron (Fe3O4) occurring in isometric
crystals, also massive, of a black color and metallic luster. It is
readily attracted by a magnet and sometimes possesses polarity, being
then called loadstone. It is an important iron ore. Called also
magnetic iron.
- A black submetallic mineral consisting of oxide of
chromium and iron; -- called also chromic iron. - A compound or salt of chromous hydroxide regarded as an
acid.
- An earthy oxide of manganese, or mixture of different oxides
and water, with some oxide of iron, and often silica, alumina, lime, or
baryta; black ocher. There are several varieties. - Plumbago, or black lead.