Quartz

Quartz is a mineral that is used for the making of crystal balls.

Empath: The Luckiest Smurf stories
In the EMPATH: The Luckiest Smurf story series, quartz is mined by the Smurfs for the creation of lenses for telescopes, microscopes, and magnifying lenses, and also for the creation of Brainy's and Narrator's glasses.