igneous
Basalt River Pebble
Mafic Igneous Rock (Fine-grained Basalt)
Hardness: 6-7 on Mohs scale. Color: Dark gray to greenish-gray. Luster: Dull or earthy. Structure: Fine-grained (aphanitic), non-crystalline visible to the naked eye. Specific Gravity: 2.8-3.0.
- Hardness
- 6-7 on Mohs scale
- Color
- Dark gray to greenish-gray
- Luster
- Dull or earthy
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Dark gray to greenish-gray. Luster: Dull or earthy. Structure: Fine-grained (aphanitic), non-crystalline visible to the naked eye. 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 water-worn and weathered in a fluvial (river) or coastal environment, giving it its smooth, rounded shape.
Uses & applications
Primarily used in construction as aggregate, road base, and concrete. In smaller forms like this, it is used for decorative landscaping, 'worry stones', or aquariums.
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
Identify in the field by its dark color, heavy weight relative to size (high density), and lack of visible crystals. Commonly found in volcanic regions or riverbeds downstream from volcanic sources. Collectors value specimens with unique weathering patterns.
