Linked from
The 11 pages that link to Monazite, each with the reason it gives.
MischmetalRelated: Its mixed rare-earth content historically supplied feedstock for mischmetal.
NeodymiumRelated: Monazite concentrates can supply neodymium among other lanthanides.
HolmiumRelated: Monazite is one of the ores from which holmium can be recovered.
ThuliumRelated: Thulium occurs in trace amounts in monazite ores.