igneous
Basalt (River Pebble)
Extrusive Mafic Igneous Rock
Hardness: 6-7 on Mohs scale. Color: Dark grey to black, weathering to brown or green. Luster: Dull/Earthy (aphanitic). Crystal structure: Fine-grained/Microcrystalline. Specific gravity: 2.8–3.0.
- Hardness
- 6-7 on Mohs scale
- Color
- Dark grey to black, weathering to brown or green
- Luster
- Dull/Earthy (aphanitic)
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Dark grey to black, weathering to brown or green. Luster: Dull/Earthy (aphanitic). Crystal structure: Fine-grained/Microcrystalline. 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 rounded and smoothed through fluvial erosion (water transport) over thousands of years.
Uses & applications
Commonly used as high-strength construction aggregate for roads and railroads, as a heat-retaining medium in 'hot stone' massage therapy, or as decorative landscaping stones.
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 (high density), dark matte color, and lack of visible individual crystals. Look for smooth, rounded shapes in riverbeds or pitted 'vesicular' textures near volcanic sites.
