A heatstone is a round or oval piece of volcanic glass that weigh anywhere from 2 to 4 pounds each. Depending on the outside temperature, a heatstone can heat anywhere from a twenty to forty foot square area. These stones last three years before they lose their warmth, and must be replaced. This fact keeps their value up in the colder regions of the world. These magical stones are formed naturally in Qadira, where these who wander the desert collect them to sell in Katheer. 
Although they are used to keep troops warm in winter battles, a heatstone cannot offer enough heat to be used as weapon. Some say that Keleshite sorcerers use heatstones as a device to allow them to listen in on conversations over long distances.