Mind Crystal (Extended)

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: If the spell has a duration of 1 minute or longer, double the spell's duration, to a maximum duration of 24 hours.