The sphere symbolizes wholeness. As a shape, the sphere is a universal symbol that represents unity and infinity, basically the whole universe.
A ball shape differs from the focused energy of a wand or egg shape crystal as it emits energy in all directions equally. Spheres make a useful tool to perceive a complete picture of yourself or situations by moving energy around and through the entire environment.
Even if you aren’t into the energetic properties of crystals, you can’t deny their beauty!