igneous
Basalt (Vesicular or Porphyritic)
Aphanitic Mafic Igneous Rock
Hardness: 5-6 Mohs. Color: Dark grey to black with light-colored phenocrysts. Luster: Dull to sub-vitreous. Crystal structure: Fine-grained matrix (aphanitic) with larger visible crystals. Specific gravity: 2.8-3.0.
- Hardness
- 5-6 Mohs
- Color
- Dark grey to black with light-colored phenocrysts
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 5-6 Mohs. Color: Dark grey to black with light-colored phenocrysts. Luster: Dull to sub-vitreous. Crystal structure: Fine-grained matrix (aphanitic) with larger visible crystals. 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 surface of a terrestrial planet or moon. Most basalt on Earth is less than 200 million years old due to tectonic recycling.
Uses & applications
Used in construction as aggregate, for paving, in the manufacturing of stone wool insulation, and occasionally as decorative polished stones or for aquarium landscaping.
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 by dark color, heavy weight (relative to size), and fine-grained texture. Often found along coastlines or in volcanic regions like Hawaii or the Pacific Northwest.
