This crackling crystal contains the essence of an untamable storm. While attuned, you gain advantage on constitution saving throws to maintain concentration on your spells. 

As an action, you can attach the shard to an wearable object 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.

This shard has 3 charges. At level 5, you can use 1 charge to cast Call Lightning. When you have access to 4th level spells, you can expend 2 charges to cast this spell at level 4, and When you have access to 5th level spells, you can expend 3 charges to cast this spell at level 5. Charges are regained after a long rest. 

When you use a Metamagic option on a spell while you are holding or wearing the shard, you can use this property:

If the damage from the spell is lightning or thunder damage, instead of rolling the dice for damage you deal the max possible damage.

(for example, if you cast Thunderwave at 3rd level, instead of rolling 4d8 you deal 32 thunder damage.)

Notes: Advantage: Constitution Saving Throws, sorcerer