Firemarbles were the primary light source for the D'ni. They are a special form of stone which glows when scratched or struck, generating a soft light. They vary in size from typical marble-sized spheres to massive globes several feet in diameter. They can be extinguished by dousing them with water.

It would appear that firemarbles to pose a fire hazard if they impact an object with sufficient force to cause them to shatter. This is evidenced by the fire in Tomahna sparked by a firemarble thrown by Saavedro, which shattered, setting a nearby curtain aflame. However, it should also be noted that the power output of detonated firemarbles likely pales in comparison to the power output of detonated powermarbles.