Smelting slag is a byproduct of the smelting process, and is composed of impurities that are removed from the ore during the smelting process. The term 'SCORIA' is used to refer to this type of slag, which is a dark-colored, vesicular, and porous rock. It is typically composed of iron, magnesium, calcium, and silicon oxides, as well as other minerals. SCORIA is often used in construction and landscaping projects, and can also be used as an aggregate for asphalt pavement.