Arcane Crystal

Arcane Crystals are remnants of the duel between Chaos and Agathon, pieces of celestial flesh resting under their blood that became the land of Amvior. Arcane Crystals is the main exported good of Gaia and they are uncommon in that regeon only. There powers are applyified based the way the gem is cut. An expirienced gemcutter can make exquisite crystals and con artist can make really simple ones, that still hold power.

A creature can use an action to attach one crystal on a weapon, spellcasting focus, holy symbol, or on a piece of jewelry. An item can only have one arcane crystal attached to it. Depending on the type of crystal they gain the bonuses specified below:

Weapon. If the crystal is attached to a weapon it counts as a magical weapon for the purpose of overcoming resistances. It also gains a bonus to damage depending on the type of the crystal.

Spellcasting Focus/Holy Symbol. If the crystal is attached to a spellcasting focus or holy symbol, damaging spells cast using this focus add a bonus to damage depending on the type of the crystal.

Piece of Jewelry. If the crystal is attached to a piece of jewelry, the unarmed strikes of the wearer gain a bonus to damage depending on the type of the crystal and they are considered magical for the purpose of overcoming resistances. If the wearer has the Spellcasting or Pact Magic feature they can give disadvantage on a saving throw against one of their spells if the target(s) have been dealt damage corresponding to the color of the crystal. The last feature can be used twice and can't be used again until the next dawn.

Arcane Crystals 

Arcane Crystals' Damage Types