Jewel of Orthon

The Jewel of Orthon is a purple gem that Rennek borrowed from Alexi. It can be used to control people from afar. It is unknown whether people have any memory of being controlled once the magic has been withdrawn.

Where There's Smoke There's a Firestarter
Rennek borrows the jewel from Alexi in order to tear the Halliwell’s apart. His exact plan was never told, however an image of Montgomery Knox appears in Alexi’s mirror when Rennek requests more time with the jewel, implying that Rennek may have controlled Knox at some point during the issue.

The Heavens Can Wait
Rennek and Alexi used the jewel on Bailey and made her suggest to Paige that she should go to Salem and try to recruit Sarah for magic school.