The silicate groups and extra ions connect the chains together. Since the chains are parallel, the crystals tend to be prismatic. The chains are arranged in parallel planes and allanite's cleavage breaks the bonds between these planes. Allanite is found as an accessory mineral in several igneous rocks such as granites, syenites, diorites and their pegmatites and in a few metamorphic rocks as small embedded grains. It forms tabular crystals that can have excellent form and character.
Color is commonly black but can be brown to brownish violet if translucent.
Luster is vitreous to greasy. Crystals are commonly opaque but can be found translucent. The terminations are usually wedge shaped, more rarely tapered pyramids. Also massive or as is most commonly the case, as embedded grains. Cleavage poor in one direction, lengthwise.