Igneous
Basalt (Water-worn)
Aphanitic Mafic Igneous Rock
Hardness: 5-6 Mohs. Color: Dark gray to black. Luster: Dull to sub-vitreous. Structure: Fine-grained (aphanitic). Cleavage: None. Specific gravity: 2.9-3.1. Surface: Smooth, rounded due to water erosion.
- Hardness
- 5-6 Mohs
- Color
- Dark gray to black
- Luster
- Dull to sub-vitreous
Identified More igneous →
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Physical properties
Hardness: 5-6 Mohs. Color: Dark gray to black. Luster: Dull to sub-vitreous. Structure: Fine-grained (aphanitic). Cleavage: None. Specific gravity: 2.9-3.1. Surface: Smooth, rounded due to water erosion.
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 shaped and polished by the abrasive action of water/sediment in a river or coastal environment.
Uses & applications
Used extensively in construction as aggregate, for road base, and in railroad ballast. Polished river stones are used in landscaping, massage therapy, and decorative crafts.
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.
Field identification & locations
Identified by its dark color, heavy weight (density), and lack of visible crystals. Commonly found in volcanic regions or in riverbeds downstream from volcanic sources.
