REE refers to rare-earth elements, mostly those belonging to the lanthanide series.
It crystallizes in the trigonal rhombohedral system and has a white vitreous appearance with a conchoidal fracture.
Zajacite is transparent with refractive indices nω = 1.483 and nε = 1.503.
It occurs as creamy to white anhedral to subhedral grains in pegmatite and aplite pods or lenses in a peralkaline igneous intrusion.
It was discovered in 1993 at Strange Lake, Quebec – Labrador, (56°20'N, 64°10'W) and was initially named for Ihor Stephan Zajac, who led the expedition responsible for its discovery, and who first recognized the presence of the new mineral.