igneous
Basalt River Stone
Aphanitic Mafic Igneous Rock (primarily Plagioclase and Pyroxene)
Hardness: 5-6 (Mohs); Color: Dark grey to charcoal black; Luster: Dull to sub-vitreous; Structure: Fine-grained (aphanitic) with rounded water-worn texture; Cleavage: None/Irregular; Specific Gravity: 2.8-3.0
- Hardness
- 5-6 (Mohs)
- Color
- Dark grey to charcoal black
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 5-6 (Mohs); Color: Dark grey to charcoal black; Luster: Dull to sub-vitreous; Structure: Fine-grained (aphanitic) with rounded water-worn texture; Cleavage: None/Irregular; Specific Gravity: 2.8-3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or near the Earth's surface. This specific specimen has been significantly rounded and smoothed by fluvial (river) or coastal erosion processes.
Uses & applications
Commonly used in landscaping as decorative river rock, in construction as road base or concrete aggregate, and sometimes in hot stone massage due to high heat retention.
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 in abundance on the Moon and Mars.
Field identification & locations
Identify in the field by its heavy weight relative to size, dark uniform color, and lack of visible crystals. Commonly found in volcanic regions or in riverbeds downstream from volcanic sources.
