The facts in theory: this tetragonal mineral with typical content of 17-40% La and 35-51% V is linked to Xenotime Group. Color is light pink to brown, transparent to lucent.
The reality in Eifel specimen: you will not see the mineral optically. Main crystal as layer is a Monazite-X, this one is encrusted with elongated Apatite at basis. The big octahedrons are Oxy-Calciobetafite (an uranium-rich Ti-dominant Pyrochlore) and between the bigger crystals in pendentives white color you will find the indicated tetragonal bipyramid of Wakefieldite-La.
Typically for Laacher See / Wingertsberg and Bellerberg location is the paragenetic with Hematite crystals. Not all but some specimen contains also the mineral Cerianite-Ce. See other picture with Monazite from Bellerberg covered by yellow clear Cerianite crystals (57% Ce, 23% Th, 3% U, 6% Ph, 11% Ca). Here together with nice yellow red colored Forsterite crystals - typically for fumarole formation.
[quote G. Blaß, for more details please ask for Eifel-CD; EDX picture as a graphic styled by origin of G.Blaß © 2020]