... black, porous light,and it's the good filter material. Lava filter material Productds description:1, appearance shape: no point granular ... film is not easy to fall off.2, porous: volcanic rock is a natural honeycomb porous, is zooglea is better growth ... plant, paper making, pharmacy, brewing, electric power, metallurgy, coal gas, textile, printing and dyeing, petroleum, chemical industry is the ideal ...