igneous
Slag
Metallurgical Slag
Hardness typically varies from 5 to 7 on the Mohs scale depending on composition; color ranges from dark grey, black, to greenish-brown; vitreous to dull luster; amorphous or glassy crystalline structure; lacks true cleavage; specific gravity is generally around 2.5 to 3.5.
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Physical properties
Hardness typically varies from 5 to 7 on the Mohs scale depending on composition; color ranges from dark grey, black, to greenish-brown; vitreous to dull luster; amorphous or glassy crystalline structure; lacks true cleavage; specific gravity is generally around 2.5 to 3.5.
Formation & geological history
Formed as a byproduct of smelting ore to purify metals, primarily iron and steel, where impurities combine with fluxes at high temperatures in a blast furnace and are cooled.
Uses & applications
Extensively used in construction as aggregate for road bases, asphalt production, cement manufacturing, railway ballast, and sometimes in landscaping.
Geological facts
Although technically a man-made industrial byproduct rather than a natural geological rock, slag is often grouped with geological aggregates and can weather to form secondary mineral assemblages over time.
Field identification & locations
Found abundantly near historical and active industrial smelting sites, steel mills, and rail lines where aggregate has been distributed. Can be identified by its vesicular (bubble-holed), glassy texture and often dense weight compared to natural sedimentary rocks.
