This gemstone contains a crystallized bit of spellcasting magic.
When you cast a spell that has a casting time of 1 action while holding the mind crystal, you can modify the spell in the way described below. You can use only a single mind crystal to modify the spell, and you can't use a mind crystal and a Metamagic option on the same spell. Once you use the mind crystal, it becomes a nonmagical gem worth 50 gp.
Modify Spell
When you roll damage for the spell, you can reroll up to three damage dice. You must use the new rolls.