igneous
Basalt River Pebble
Basalt (Aphanitic Mafic Igneous Rock)
Hardness: 6-7 on Mohs scale; Color: Dark grey to black; Luster: Dull to matte (waxy when wet); Crystal Structure: Fine-grained (aphanitic), typically invisible to the naked eye; Cleavage: None/Irregular; Specific Gravity: 2.8–3.0.
- Hardness
- 6-7 on Mohs scale
- Color
- Dark grey to black
- Luster
- Dull to matte (waxy when wet)
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Dark grey to black; Luster: Dull to matte (waxy when wet); Crystal Structure: Fine-grained (aphanitic), typically invisible to the naked eye; Cleavage: None/Irregular; Specific Gravity: 2.8–3.0.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava exposed at or very near the surface of a terrestrial planet or a moon. This specimen has been rounded by fluvial (river) or coastal erosion processes.
Uses & applications
Basalt is used extensively in construction (crushed stone, concrete aggregate), as 'hot stones' for massage therapy, and occasionally in landscaping or aquarium decor.
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 common on the Moon and Mars.
Field identification & locations
Field identification features include its dark color, heavy weight for its size (high density), and lack of visible crystals. Commonly found in volcanic regions or as weathered cobbles in riverbeds and on beaches.
