Elemental Essence Shard

From Tasha's Cauldron of Everything, page 127.

Description
Wondrous item, rare (requires attunement by a sorcerer)

This crackling crystal contains the essence of an elemental plane. As an action, you can attack 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 while you hold or wear it.

Roll a d4 and consult the Elemental Essence Shards table to determine the shard's essence and property. When you use a Metamagic option on a spell while you are holding or wearing a shard, you can use that property.