igneous
Vesicular Basalt
Aphanitic Mafic Igneous Rock (with vesicles)
Porous texture due to gas bubbles (vesicles), color: grey to black, hardness: 5-6 Mohs scale, luster: dull/earthy, crystal structure: fine-grained (aphanitic), specific gravity: 2.8-3.0.
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Physical properties
Porous texture due to gas bubbles (vesicles), color: grey to black, hardness: 5-6 Mohs scale, luster: dull/earthy, 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 at the Earth's surface. The holes (vesicles) are created by trapped gas bubbles that escaped as the lava solidified.
Uses & applications
Used in construction for road base, concrete aggregate, railroad ballast, and ground cover in landscaping. Highly porous varieties are used as 'lava rocks' for gas grills.
Geological facts
Basalt is the most common rock in Earth's crust and makes up most of the ocean floor. It is also found extensively on the Moon and Mars.
Field identification & locations
Identify by its dark color, heavy weight (relative to size, unless very porous), and characteristic pit-marks or holes. Commonly found in volcanic fields, oceanic islands, and mid-ocean ridges.
