Coalstone

You transform the fire agate you hold in your hand into a coalstone, a small stone that sheds bright light to a 10-foot radius and dim light to a further 10 feet. This coalstone is hot enough that, if touched to bare skin or a flammable object for a full round, it inflicts 1 fire damage and will set that object alight. The coalstone can be placed inside of a fireproof container when not in use.