Amber eye

Amber eye: This amber gem was extracted  from the eyes of a clockwork centipede larvae. Looking closely into the gem you can see flames dancing inside it. To maintain its properties, the gem must be placed in a pit of fire for 1 hour, once a month.

As an action the character holding the gem can create a beam that ignites with radiant energy. 

Igniting Beam (Recharge 5–6). The gem fires a beam of energy in a 60-foot line that is 10 feet wide. Each creature in the line must make a DC 15 Dexterity saving throw, taking 15 (3d10) radiant damage on a failed save, or half as much damage on a successful one. A creature reduced to 0 hit points by this beam catches fire.

Notes: Attunement by a spell caster