melaconite

from The Century Dictionary.

• noun A black or grayish-black, impure, earthy (also crystallized) oxid of copper, found in Vesuvian lava (there called tenorite) and abundantly at Keweenaw Point, Lake Superior. In the latter case it is the result of the decomposition of other ores.

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

• noun (Min.) An earthy black oxide of copper, arising from the decomposition of other ores.

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

• noun mineralogy An earthy black oxide of copper, arising from the decomposition of other ores.