Coronadite

Formula: Pb(Mn4+6Mn3+2)O16 multiple oxide, cryptomelane group
Specific gravity: 5.44
Hardness: 4½ to 5
Streak: Brownish black
Colour: Dark grey to black
Environments:

Sedimentary environments
Metamorphic environments
Hydrothermal environments
Hot springs

Coronadite occurs as a primary mineral in hydrothermal veins or from hot springs, and it is of secondary origin in oxidized zones above manganese deposits and bedded sedimentary rocks. hollandite, pyrolusite and other manganese oxides are common associates.
Common impurities: Fe,Al,H2O