Ignium

Deep beneath the earth, in the fiery roots of every volcano, the raw heat of the elemental plane of fire seeps through into the prime material. Bound by the forces of pressure and time, the surrounding rock will eventually stabilize into a magmatic yet sturdy stone substance known as Ignium.
  Description: Ignium is a solid stone with a turbulent fiery force visible just beneath the surface. Despite approaching the melting point of stone, it remains a sturdy building material. The intense heat spills out into the surrounding area, driving up the surrounding temperature and searing all that it comes in contact with.
  Natural Properties: Ignium is immune to any effect that would harm it due to cold. It emits bright light in a 10-foot radius and dim light for an additional 10 feet. It ignites flammable objects it comes in contact with, and deals 1d6 fire damage to creatures it comes in contact with. Worn and carried items usually include padding that protects the owner from this effect. Weapons. Weapons made of ignium deal fire damage rather than their regular damage type, and deal additional 1d6 fire damage from the natural property of ignium. Armour. Creatures wearing armour made of ignium have resistance to cold damage. (Striking a creature wearing ignium armour does not provoke the damaging or burning natural property.)
  Example Item: Eternal Furnace. A furnace containing a layer of ignium will never burn out, even if fuel is not provided.