ilmenium

from The Century Dictionary.

• noun A name given by Hermann to an element supposed by him to be present in the æschynite from the Ilmen mountains (in the southern Urals), also in yttrotantalite and some related minerals. His conclusions have not been accepted by other chemists.

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

• noun (Chem.) A supposed element claimed to have been discovered by R.Harmann.

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

• noun obsolete A supposed chemical element, later found to be a mixture of niobium and tantalum.