igneous
Basalt (Worn Cobble / Artifact)
Aphanitic Extrusive Igneous Rock
Hardness of 6 on the Mohs scale; dark gray to brown color due to weathering; fine-grained (aphanitic) crystal structure; dull luster.
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Physical properties
Hardness of 6 on the Mohs scale; dark gray to brown color due to weathering; fine-grained (aphanitic) crystal structure; dull luster.
Formation & geological history
Formed from the rapid cooling of magnesium- and iron-rich lava exposed at or very near the Earth's surface.
Uses & applications
Commonly used in construction, road aggregate, and historically shaped by indigenous peoples into tools such as pestles or celts due to its density and toughness.
Geological facts
Basalt is the most common rock type in the Earth's crust underlying the oceans and forming much of volcanic island chains.
Field identification & locations
Found worldwide in volcanic regions and riverbeds where water action rounds the dense stone. Identify by its fine grain, high density, and dark interior exposed beneath weathered surfaces.
