Crystals are blue rocks, also known as Hextech, that are used by Piltover and Zaun, they they hold tremendous power and can be used to achieve a great number of things. They were discovered by Jayce in his early years when him and his mother were lost in the snow region. His mother collapsed and when Jayce call for help, a strange mage appears. Using a shard of a Crystal, the mage accesses the magic within and uses it to teleport himself, Jayce and his mother to a warmer climate, thus saving their lives.
In his later years Jayce acquires some crystals and begin experimenting with combining magic and science. With the help of Viktor he succeeds, creating a energy source for all of Piltover. He also uses them to create a Teleportation contraption that Piltover uses to transport goods across the globe as well as bring in tourists.
In her younger years when Jinx was known as Powder, her and her adoptive family broke into Jayce's apartment to steal anything valuable. Powder steals the crystals, not knowing the power they hold. When Jayce arrives