Elemental Sheath

You touch a weapon with one of the corresponding gemstones and sheath it with elemental power. When you cast this spell you choose one damage type from the corresponding table and create a glowing sheath of energy around a weapon you are holding. The first melee attack that hits with the weapon you chose, deals an extra 2d8 of the selected damage type to the creature and the sheath of energy fades from the weapon. As a bonus action during the spell's duration, you can sheath the weapon in the damage type chosen when you cast this spell originally. Additionally, for the duration, you can use your spellcasting ability instead of Strength for the attack and damage rolls of melee attacks using that weapon.