igneous
Basalt (River Rock)
Basalt
Hardness: 6.0; Color: Dark grey to black, weathering to brownish-tan; Luster: Dull or earthy; Structure: Fine-grained (aphanitic); Specific Gravity: 2.8–3.0.
- Hardness
- 6
- Color
- Dark grey to black, weathering to brownish-tan
- Luster
- Dull or earthy
Identified More igneous →
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Physical properties
Hardness: 6.0; Color: Dark grey to black, weathering to brownish-tan; Luster: Dull or earthy; Structure: Fine-grained (aphanitic); 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 specimen appears water-worn, indicating a long secondary history in a fluvial (river) environment.
Uses & applications
Commonly used as aggregate in construction, road base, and railroad ballast. Exceptionally smooth pieces are used in decorative landscaping and stone massage.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. It is cũng the primary rock type on the Moon and Mars.
Field identification & locations
Identify by its weight (heavy for its size), dark interior, and fine-grained texture lacking visible crystals. Commonly found in former volcanic regions and riverbeds.
