igneous
River Rock (Basalt)
Aphanitic Basaltic Rock
Hardness: 6.0-7.0 (Mohs scale). Color: Medium to dark grey. Luster: Dull/earthy (weathered surface). Structure: Microcrystalline to aphanitic (fine-grained). Cleavage: None. Specific Gravity: 2.8-3.0.
- Hardness
- 6
- Color
- Medium to dark grey
- Luster
- Dull/earthy (weathered surface)
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Physical properties
Hardness: 6.0-7.0 (Mohs scale). Color: Medium to dark grey. Luster: Dull/earthy (weathered surface). Structure: Microcrystalline to aphanitic (fine-grained). Cleavage: None. 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 transport-weathered and rounded through fluvial (river) or glacial action, likely over thousands of years.
Uses & applications
Commonly used in landscaping (mulch replacement), drainage systems, construction aggregate, and occasionally for rock painting or spa 'hot stones'.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. Large-scale basaltic lava flows can form unique hexagonal columns, such as those at the Giant's Causeway.
Field identification & locations
Identify in the field by its heavy weight (high density), dark interior color, and smooth, water-worn texture. It is a 'clastic' river stone found in stream beds, beaches, and landscaping supply yards globally.
