Each Gem is a small, smooth oval, and known by their respective powers. Each of the Gems represents a different characteristic of Existence and possessing any single Gem grants the possessor the ability to potentially command whatever aspect of Existence the Gem represents. The Gems are indestructible but not immutable. On two occasions one or more of the Gems have appeared in the form of deep pink spheres that were several feet in diameter.
On other occasions the gems have appeared in their normal shape but with different coloring (i.e. when the Soul Gem appeared to be red when worn by the Gardener). In the Ultraverse, the merged Gems, Nemesis, were once again separated after a climactic battle with Ultraforce and the Avengers. The Space, Power, Soul, and Mind gems morph into humanoid beings. The nature of these beings is not known, nor how these beings returned to their original forms.