igneous
Basalt
Basalt (composition predominately plagioclase feldspar and pyroxene)
Hardness: 6 (Mohs), Color: dark grey to black, Luster: dull to sub-metallic, Crystal Structure: fine-grained (aphanitic), Specific Gravity: 2.8–3.0
Identified More igneous →
Explore Basalt in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 6 (Mohs), Color: dark grey to black, Luster: dull to sub-metallic, Crystal 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 exposed at or very near the surface of a terrestrial planet or a moon. It is the most common volcanic rock on Earth.
Uses & applications
Extensively used in construction, specifically as road base, railroad ballast, and aggregate in concrete. High-quality specimens are used in stone masonry and floor tiles.
Geological facts
Basalt makes up most of the Earth's oceanic crust. It is also found on the Moon and Mars. On Earth, it can form massive columns such as the Giant's Causeway in Northern Ireland.
Field identification & locations
Identify by its dark color, heavy weight (dense), and fine-grained texture. It often feels slightly gritty and may contain small vesicles (holes) or phenocrysts.
