igneous
Basalt Pebble
Aphanitic Mafic Igneous Rock
Hardness of 6 on the Mohs scale, dark gray to black color, dull to sub-metamorphic luster, fine-grained (aphanitic) crystal structure, high specific gravity around 2.8-3.0.
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Physical properties
Hardness of 6 on the Mohs scale, dark gray to black color, dull to sub-metamorphic luster, fine-grained (aphanitic) crystal structure, high specific gravity around 2.8-3.0.
Formation & geological history
Formed from the rapid cooling of low-viscosity, iron- and magnesium-rich lava exposed at or very near the Earth's surface.
Uses & applications
Used in construction, aggregate for roadbeds, railroad ballast, and decorative landscaping.
Geological facts
Basalt is the most common rock type in the Earth's crust, particularly making up most of the oceanic crust and volcanic islands like Hawaii.
Field identification & locations
Easily identified by its dark, fine-grained appearance and heavy feel. Often found rounded in riverbeds and beaches due to water transport.
