Rock Identifier
Basalt with Weathering Crust (Extrusive mafic volcanic rock) — igneous
igneous

Basalt with Weathering Crust

Extrusive mafic volcanic rock

Hardness: 5-6 Mohs. Color: Dark grey to black interior with a brownish-tan weathered exterior (oxidized). Luster: Dull/Earthy. Structure: Fine-grained (aphanitic). Specific gravity: 2.8-3.0.

Hardness
5-6 Mohs
Luster
Dull/Earthy
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Physical properties

Hardness: 5-6 Mohs. Color: Dark grey to black interior with a brownish-tan weathered exterior (oxidized). Luster: Dull/Earthy. Structure: Fine-grained (aphanitic). Specific gravity: 2.8-3.0.

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava at or near the Earth's surface. The brownish coating is caused by chemical weathering (oxidation) of iron-bearing minerals like olivine and pyroxene.

Uses & applications

Used primarily in construction (crushed stone, road base), as a dimension stone, and in the production of stone wool insulation.

Geological facts

Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. It is also found in abundance on the Moon and Mars.

Field identification & locations

Identify in the field by its high density and dark interior visible when chipped. It is commonly found in volcanic regions or ancient rift zones. Small, weathered hand samples are ubiquitous in many geological settings.

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