The HPC Fire Black Lava Rock provides a high quality fire media for use with your gas fire pit or fireplace. Lava rock is proven to increase combustion efficiency and it enhances the look of your fire feature. The organic material is naturally resistant to high heat while the natural black color rock creates a realistic volcanic visual. The rocks range from 1 to 2 inches in size and comes in a 1/2 cubic foot bag or roughly 23 pounds.