Midwest Hearth Natural Lava Granules will instantly renew and enhance your fireplace. What is lava rock: – Naturally occurring, these lava rocks are formed as volcanic magma rises to the surface, cools and releases gases which gives these rocks their coarse surface. – Because they are volcanic, they can withstand extremely high temperatures without sustaining any damage or crumbling. Features: ✔ All natural – No added stains or colorants. ✔ Withstands extremely high temperatures. ✔ Will not break down or crumble. ✔ Appropriate size granules for indoor gas appliances. ✔ Adds realism to your fireplace. ✔ Hides unsightly burner pans, cracked fire brick, and more. ✔ Coarse surface works well with optional rock wool and glowing embers. ✔ Generous bag size is adequate for most fireplace log sets. ✔ Works with both Natural Gas and Propane appliances.