igneous
Basalt pebble
Basalt (mafic extrusive rock)
Mohs hardness 6-7, dark grey to dull brown color, fine-grained (aphanitic) texture, matte luster, high density (specific gravity 2.8-3.0)
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Physical properties
Mohs hardness 6-7, dark grey to dull brown color, fine-grained (aphanitic) texture, matte luster, high density (specific gravity 2.8-3.0)
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. Often found in seafloor spreading centers and volcanic islands.
Uses & applications
Used as aggregate in construction, road base, asphalt, and sometimes as smooth river stones for decoration or massage therapy.
Geological facts
Basalt is the most common rock type in the Earth's crust and even makes up the 'maria' (dark plains) on the Moon.
Field identification & locations
Identify by its weight (heavy for its size), dark color, and fine-grained texture with no visible individual crystals to the naked eye. Commonly found on beaches or in riverbeds.
