igneous
Basalt Pebble
Extrusive Igneous Rock
Hardness of 6 on the Mohs scale, dark gray to black in color, fine-grained to aphanitic texture, dull to sub-metallic luster, specific gravity around 2.8 - 3.0
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Physical properties
Hardness of 6 on the Mohs scale, dark gray to black in color, fine-grained to aphanitic texture, dull to sub-metallic luster, specific gravity around 2.8 - 3.0
Formation & geological history
Formed from the rapid cooling of low-viscosity lava rich in iron and magnesium exposed at or very near the Earth's surface, often shaped into a smooth pebble by wave action on a beach.
Uses & applications
Used in construction, as aggregate in concrete, road base, and occasionally in landscaping or as a tumbling stone.
Geological facts
Basalt is the most common rock type in the Earth's crust underlying the ocean basins, and it is also found extensively on the Moon and Mars.
Field identification & locations
Easily identified in the field by its dark, heavy, fine-grained appearance, often with small vesicular holes from trapped volcanic gas bubbles.
