igneous
Basalt (River Stone)
Extrusive mafic igneous rock
Hardness: 6.0; Color: Dark grey to black; Luster: Dull/Sub-metallic; Structure: Fine-grained (aphanitic) with possible inclusions; Specific Gravity: 2.8-3.0
- Hardness
- 6
- Color
- Dark grey to black
- Luster
- Dull/Sub-metallic
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Physical properties
Hardness: 6.0; Color: Dark grey to black; Luster: Dull/Sub-metallic; Structure: Fine-grained (aphanitic) with possible inclusions; 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 specimen has been rounded by fluvial (river) or glacial movement.
Uses & applications
Mainly used as aggregate in construction, road base, and railroad ballast. Small weathered pebbles are often used in landscaping or massage therapy.
Geological facts
Basalt is the most common rock type in the Earth's crust and also makes up most of the ocean floor. It is found on the Moon and Mars as well.
Field identification & locations
Identify by its dark color, heavy weight for its size, and lack of visible large crystals. Commonly found in volcanic regions or riverbeds downstream from volcanic sites.
