igneous
Basalt River Stone (Tumbled)
Basalt (Mafic Extrusive Igneous Rock)
Hardness: 6-7 on Mohs scale. Color: Dark grey to black, often weathering to greyish-white on higher surfaces. Luster: Dull to sub-metallic. Crystal structure: Aphanitic (fine-grained) to porphyritic. Specific gravity: 2.8-3.0.
- Hardness
- 6-7 on Mohs scale
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Dark grey to black, often weathering to greyish-white on higher surfaces. Luster: Dull to sub-metallic. Crystal structure: Aphanitic (fine-grained) to porphyritic. 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. This specific specimen has been Rounded and smoothed by fluvial (river) or glacial abrasion over thousands of years.
Uses & applications
Extensively used in construction as aggregate for concrete and asphalt, railroad ballast, and stone dust. Tumbled specimens are popular in spa treatments (hot stone massage) and decorative landscaping.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. It is also found on the Moon and Mars. It covers roughly 70% of Earth's surface.
Field identification & locations
Identify in the field by its dark color, heavy weight (density), and fine-grained texture. It will not react with acid. Commonly found in volcanic fields, riverbeds, and coastal regions.
