The legendary Gem of Cyttorak was once believed to possess mystical properties. However, it now emits a very distinctive radiation.
The radiation emitted by the gem is able to enhance the powers of any mutant exposed to it, to the point of causing their bodies to change in order to adjust to the enhancement and power boost, such as when Sabretooth was exposed and became more beast-like than human. Or when Cyclops and Havok were enhanced and gained control of their powers.
Such mutants exposed to the gem's radiation include: