igneous
Basalt Pebble
Basalt (Mafic Igneous Rock)
Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal Structure: Fine-grained (aphanitic) to glassy; Cleavage: None; Specific Gravity: 2.8–3.0
- Hardness
- 6 (Mohs scale)
- Color
- Dark grey to black
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal Structure: Fine-grained (aphanitic) to glassy; Cleavage: None; 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 surface of a terrestrial planet or a moon. This specific pebble shows signs of water-erosion and quartz/calcite veining.
Uses & applications
Crushed basalt is used in construction for road base, concrete aggregate, and railroad ballast. Larger pieces are used in landscaping and shoreline protection.
Geological facts
Basalt is the most common rock type in Earth's crust and covers most of the ocean floor. It is also found extensively on the Moon and Mars.
Field identification & locations
Identify by its dark color, heavy weight for its size (density), and fine-grained texture. It often features small white veins where minerals filled cracks after the initial cooling.
