Gadolinite

[gædәlinait]

(noun.) a mineral that is a source of rare earths; consists of silicates of iron and beryllium and cerium and yttrium and erbium.

Typed by Benjamin--From WordNet

(n.) A mineral of a nearly black color and vitreous luster, and consisting principally of the silicates of yttrium, cerium, and iron.

Checker: Virgil

n. a silicate of the yttrium and cerium metals containing also beryllium and iron.

Checker: Trent