Share Crystal (シェアクリスタル, Shea Kurisutaru), also called Sharicite, is the crystallized faith of people in a CPU. It is used mostly to recharge a weakened CPU's energy. It takes immense time and effort to create, and only Oracles know the complex, but safe manufacturing process. Contrary to popular belief, equipping it does not teach any magic or allow one to summon a CPU in battle.
A Share Crystal is also demonstrated as a weapon and means to restore faith within a CPU. An example of it as a weapon would be when Nepgear uses the Share Crystal to blind CFW Judge and escape the Gamindustri Graveyard. An example of it as a means to restore faith within a CPU is when Nepgear was momentarily able to abide Rom's brainwashing, a result of "lack of faith," and try to convince her to return her back to herself.
If a CPU travels into a different dimension (bar outsider CPUs going into the Hyperdimension), they will need to find a Share Crystal in order to regain their ability to use Hard Drive Divinity.
Uzume Tennouboshi uses share crystals to transform in Megadimension Neptunia VII. She can also use it to create a sharing field. Additionally in Megadimension Neptunia VII, the animation of the CPUs and CPU candidates show the CPU in question using a share crystal. In the Zero Dimension, a large amount of share crystals in a location will make the location rather scenic and full of life.