Weight: ½ lb.
Estimated Value (Sane Cost Guide): 250 gp
DMG Value:
101 gp - 500 gp
A mind crystal contains sorcerous potential, allowing a user to apply Metamagic to a spell as you cast it. For the non-sorcerers among us, Metamagic allows you to tweak and alter a spell to better suit your needs, such as extending its duration or increasing its range. While Metamagic is a sorcerer class feature that needs sorcery points to use, mind crystals are single-use items that can be used by anyone who can cast a spell.
A careful mind crystal allows up to three creatures within a spell's area of effect to automatically succeed on their saving throws against the spell. For spells like fireball, Careful Spell isn’t quite as potent as the School of Evocation wizard’s Sculpt Spells feature, so use this item on spells where a successful save spares the target of all negative effects.
Spell suggestions: confusion, entangle, faerie fire, fear, hypnotic pattern
Source: Phandelver and Below: The Shattered Obelisk