Lava Rock that comes in a Five Pound box and used within the Gas Log Sets within many manufacturers of stoves and fireplaces to enhance the gas fire to appear more natura and to renew and replace the original rocks that come with gas log sets. It is also used to decorate the firebox of both NG and LP stoves and fireplaces. You should layer the lava rocks in an even layer over sand or vermiculite in the firebox to help restore it to a new state or reclaim the realism of the fire. Mostly black in color with some reddish-brown mixed in