lanthanite

from The Century Dictionary.

• noun A rare basic carbonate of lanthanum, occurring in thin tabular crystals of a white or nearly white color.

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

• noun (Min.) Hydrous carbonate of lanthanum, found in tabular white crystals.

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

• noun mineralogy A radioactive mineral, a carbonate of the rare earth elements lanthanum, cerium, and neodymium.