Antimagic Stone

This stone is covered with inlaid bronze bands and is perfectly round, except for three small indents where the thumb, index and middle fingers can fit. This stone has 3 charges. While holding it you can use an action to squeeze the stone and expend 1 of its charges to cast the Antimagic field spell from it. The field is focused on the stone which can be passed between creatures. Unlike the usual spell it does not require concentration and lasts only 1 minute.

Whenever you expend a charge, roll a d20. On a 1, the stone explodes, failing to cast the spell and causing 8d8 fire damage to the creature holding it. The stone is destroyed. On expending the final charge, if the spell is successfully cast this explosion is guaranteed when the duration of the spell ends.