Noun
A mineral of a nearly black color and vitreous luster, and consisting principally of the silicates of yttrium, cerium, and iron.
Source: Webster's dictionarySome of these have a rare-earth composition similar to that found in xenotime or gadolinite. Source: Internet
This color behavior is similar to what Mosander and the other early workers in the lanthanides would have seen in their extracts from the gadolinite minerals of Ytterby. Source: Internet