Hi Doc, My brother-in-law says that lava rocks are the best way to spread the heat in a gas barbecue. He's covered the steel plate under his cooking grills with lava rock and says that it works better. He is correct about little else in life; could he be right about this?
Funny, we spend thirty years in the barbecue business trying to get away from an under-performing material and some people want to drag us backwards. Sure, lava rock does a fine job of spreading heat, it even does a decent job of incinerating the drippings that fall down from your food.
Where lava rock truly fails is in its tendency to soak up the drippings like a sponge. Some of us older grillers will remember epic grease fires in our barbecues; not from the food we're cooking today but from the grease-choked lava rock that had been sponging up drippings from cookouts in the past. They become little grease sponges. Bottom line: your brother-in-law is an unsophisticated Luddite.