igneous
Dark basalt or industrial slag (tentative)
Basalt; predominantly plagioclase and pyroxene, possibly with olivine
AI-generated identification · may be incorrectBlack to dark gray, fine-grained, dull to weakly glassy luster, irregular massive texture, and no obvious cleavage; typical hardness about 5–6 Mohs and specific gravity 2.8–3.1. The rounded, glossy surface could also indicate weathered furnace slag rather than natural basalt.
Identified More igneous →
Explore Dark basalt or industrial slag (tentative) in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Black to dark gray, fine-grained, dull to weakly glassy luster, irregular massive texture, and no obvious cleavage; typical hardness about 5–6 Mohs and specific gravity 2.8–3.1. The rounded, glossy surface could also indicate weathered furnace slag rather than natural basalt.
Formation & geological history
Basalt forms when mafic lava rapidly cools at or near Earth’s surface, ranging from Precambrian to modern volcanic ages. Slag is human-produced molten industrial waste and can contain bubbles, glass, and metallic-looking inclusions.
Uses & applications
Basalt is used as crushed aggregate, roadstone, railroad ballast, and occasionally dimension stone; attractive specimens are collected. Slag has little geological or commercial value except as an industrial-history collectible.
Geological facts
The image lacks scale and diagnostic fresh surfaces, so basalt versus slag cannot be confirmed visually. Vesicles, flow texture, and consistent fine grains favor basalt; abundant glass, bubbles, or metal beads favor slag.
Field identification & locations
Common basalt occurs in volcanic regions and oceanic crust; slag is common near historic furnaces, mines, and railways. A streak test, magnet test, close inspection for vesicles, and a fresh broken surface would help distinguish them.
