Dry ice, otherwise known as Venrestone, is a white mineral that can be found in cold settings, often near hot springs and streams. It has the natural property of absorbing heat from the surrounding environment, until it reaches an internal temperature of 1085 C (1985 F) it stops absorbing heat from objects cooler than itself. When exposed to water containing certain molds and algae, it releases the stored up heat into the water, enough to create a hot spring or stream, until it reaches room temperature.
Venrestone has been known to single handedly create arctic regions in otherwise temperate locations, albeit, one peppered with hot springs. It is also is mined for it’s cooling and heating effects, allowing the production of ice, frozen desserts, air conditioning, and refrigeration.
Venrestone can be held by hand, but is cold enough that it starts to burn fairly quickly. A person handling it would want to use gloves. If worked however, it can be forged carefully into almost any shape, or even into other materials, provided that the craftsman is skilled enough. Alchemical substances are rare because of it's high value as a material, however it can be used in a salve to pull heat from a wound.