igneous
Basalt Pebble with Quartz Veining
Basalt (extrusive volcanic rock)
Hardness: 6-7 (Mohs); Color: Dark grey to charcoal blue; Luster: Dull/Matte; Structure: Fine-grained aphanitic with secondary crystalline veins; Cleavage: None/Conchoidal
- Hardness
- 6-7 (Mohs)
- Color
- Dark grey to charcoal blue
- Luster
- Dull/Matte
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Physical properties
Hardness: 6-7 (Mohs); Color: Dark grey to charcoal blue; Luster: Dull/Matte; Structure: Fine-grained aphanitic with secondary crystalline veins; Cleavage: None/Conchoidal
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. The white lines are secondary quartz or calcite veins that filled fractures through hydrothermal activity.
Uses & applications
Commonly used in landscaping, as aquarium decor, or as aggregate in construction; highly rounded pebbles are used in massage therapy (hot 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 extensively on the Moon and Mars.
Field identification & locations
Identify by its heavy weight (high density), dark color, and fine grain. Veined specimens like this are common on high-energy beaches or in riverbeds where water has eroded and polished the stone.
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