Rogue stone

A rogue stone (sometimes written roguestone) was a small, extremely rare magical gemstone with a tendency to cause wild magic.

Description
Rogue stones were filled with rainbow colors that flowed as if in liquid, slowly swirling iridescently, when exposed to sunlight. They were extremely rare and seemed to repel each other&mdash;no two rogue stones where ever found in the same place at the same time. Single stones have been found in treasure hoards, cold regions, and sunk in swamps, but evidence about what type of rock they occurred in was inconclusive. Rogue stones were easily faceted along natural planes and the resulting faces gave the stones their iridescent property. A typical specimen had a base value of 5,000 gp.

Powers
Rogue stones were used to cast the gemjump spell. Rogue stones did not have a detectable magic aura except at the time gemjump spell was being cast, and they were not destroyed or consumed by the initial enchantment or the activation of the spell.

The presence of a rogue stone within 20 ft (6.1 m) of a spell effect (either near the caster or the target, if any) increased the chances of that magic going wild or failing. At the recipient end, it decreased the chances of the target resisting or overcoming the magic effect, if applicable.