Depending on the jewel, that can be +1 to +20.
“Maybe Ill roll up a fire using mage so I can avenge my paladin.”
i would stat it like the rod of 7 parts artifact -- Pommel is the jaw bone of a lich ( power:detect undead 3xday cast at 18th level,Hilt - cast of mithral ( power: speak with dead 2xday cast at 18th level - Diamond dagger blade ( power: operates as a hat of difference - necromancer- allowing user to put any portion of experience they earn into it to attain levels as a necromancer) the pommel acts as a compass to locate the hilt and the hilt will locate the blade. pommel and hilt together will give the user +1 intelligence in addition to the other powers and the hilt and blade will give the user the ability of a scroll of protection from undead 1xday and all 3 pieces together will become a +3 dagger with the ability to charm undead as per the spell cast at 18th level 3xday