A incombustible form of calcium-magnesium-silicate used as a heat-resistant or insulating material. Mixed with cement or plaster, it was commonly used to form slabs or boards for kiln insulation and the hand forming of glass such as in marver plates. Asbestos dust can settle in the lungs and promote cancer and silicosis. It can be destroyed in the furnace if added to the batch: it loses its crystalline form and becomes part of the glass.