igneous
Basalt
Basalt (containing plagioclase, pyroxene, and olivine)
Hardness: 6 (Mohs scale), Color: Dark grey to black, Luster: Dull/earthy, Crystal Structure: Aphanitic (fine-grained), Specific Gravity: 2.8 - 3.0
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Physical properties
Hardness: 6 (Mohs scale), Color: Dark grey to black, Luster: Dull/earthy, Crystal Structure: Aphanitic (fine-grained), Specific Gravity: 2.8 - 3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava exposed at or very near the surface of a terrestrial planet or a moon. It is the most common rock type in Earth's crust.
Uses & applications
Used primarily as crushed stone for road base, railroad ballast, and concrete aggregate. It is also used for building blocks and in the manufacture of stone wool insulation.
Geological facts
Basalt makes up most of the ocean floor. It is found on the Moon and Mars too. The iconic Giant's Causeway in Northern Ireland is made of columnar basalt joints formed by cooling lava.
Field identification & locations
Identify by its dark color, high density, and fine-grained texture. It often feels heavy for its size. Look for it in volcanic regions, near oceanic ridges, or as rounded pebbles in riverbeds.
