metacinnabarite

from The Century Dictionary.

• noun Native mercuric sulphid, crystallizing in tetrahedral crystals, resembling those of the zinc sulphid sphalerite, also occurring massive of a black or grayish-black color. It is found with the red mercuric sulphid cinnabar in California.

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

• noun (Min.) Sulphide of mercury in isometric form and black in color.

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

• noun mineralogy sulphide of mercury in a black isometric form