igneous
Smelter Slag
Anthropogenic Silicate Slag
Hardness varies between 5 and 6 on the Mohs scale, color ranges from dark gray, black, to greenish or blue, luster is typically vitreous to dull, structure is usually amorphous/glassy or vesicular with trapped gas bubbles, specific gravity ranges from 2.5 to 3.5.
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Physical properties
Hardness varies between 5 and 6 on the Mohs scale, color ranges from dark gray, black, to greenish or blue, luster is typically vitreous to dull, structure is usually amorphous/glassy or vesicular with trapped gas bubbles, specific gravity ranges from 2.5 to 3.5.
Formation & geological history
Formed as a by-product of the smelting process of ore to purify metals such as iron, copper, lead, or steel. It is created artificially at high temperatures in industrial furnaces when fluxes combine with unwanted impurities.
Uses & applications
Frequently used as road aggregate, in concrete production, as railroad ballast, abrasive grit for sandblasting, and in manufacturing mineral wool insulation.
Geological facts
Although technically an anthropogenic (man-made) material rather than a naturally occurring geological formation, slag is often studied alongside igneous rocks due to its glassy, silicious nature and is commonly included in historical educational rock and mineral kits.
Field identification & locations
Can be identified by its glassy or vesicular texture, presence of micro-bubbles (vesicles), lack of natural crystalline structure typical of magmatic rocks, and frequent association with historical mining and smelting sites worldwide.
