stilpnomelane

from The Century Dictionary.

• noun A black, greenish-black, or bronze-colored mineral occurring in foliated plates or thin scales sometimes forming a velvety coating (the variety chalcodite), also in fibrous forms. It is essentially a hydrous silicate of iron.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Min.) A black or greenish black mineral occurring in foliated flates, also in velvety bronze-colored incrustations. It is a hydrous silicate of iron and alumina.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun mineralogy A metamorphic phyllosilicate mineral of the mica group, having the chemical formula K(Fe2+,Mg,Fe3+)8(Si,Al)12(O,OH)27.