Epididymite forms a wide range of habits and this can lead to confusion in identification. Its most popular habit, which makes for easy identification, is its twin . It forms six sided tabular trillings similar to the classic aragonite twins. The twins are usually cloudy but they are generally well formed. Also fishtail twins are quite interesting as well.
Dimorphous minerals are minerals that share the same chemistry, but have different structures.
Epididymite's structure is orthorhombic and eudidymite's structure is monoclinic , symmetrically speaking. Color is usually white or colorless, but can be pale gray, blue, yellow or violet. Luster is vitreous to silky. Crystals are transparent to translucent. Crystal System is orthorhombic.