Real Fyre Lava-Fyre Coals - LFC-10 can help give your gas fireplace a realistic looking flame and are a perfect complement to Peterson gas logs. These lava coals can also be used to cover the floor of fireplace giving it a lava rock surface. Real Fyre Lava-Fyre Coals - LFC-10 can be used to fill under the fire glass or in the center of the fire. The rocks are naturally formed and come in various shapes. Real Fyre Lava-Fyre Coals - LFC-10 average 1", but can come vary from 1/2" to 1 1/2".