Source: Tasha's Cauldron of Everything

Wondrous item, rare (requires attunement by a sorcerer)

This crystal is a solidified shard of the Astral Plane, swirling with silver mist. As an action, you can attach the shard to a Tiny object (such as a weapon or a piece of jewelry) or detach it. It falls off if your attunement to it ends. You can use the shard as a spellcasting focus for your sorcerer spells while you hold or wear it.

When you use a Metamagic option on a spell while you are holding or wearing the shard, immediately after casting the spell you can teleport to an unoccupied space you can see within 30 feet of you.