igneous
Basalt with Olivine Phenocrysts
Aphanitic Mafic Volcanic Rock (Basalt)
Hardness: 6-7 (Mohs); Color: Dark grey to black matrix with tiny green/yellow mineral inclusions; Luster: Dull/earthy matrix with vitreous inclusions; Structure: Fine-grained aphanitic matrix; Specific Gravity: 2.8-3.0.
- Hardness
- 6-7 (Mohs)
- Luster
- Dull/earthy matrix with vitreous inclusions
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Physical properties
Hardness: 6-7 (Mohs); Color: Dark grey to black matrix with tiny green/yellow mineral inclusions; Luster: Dull/earthy matrix with vitreous inclusions; Structure: Fine-grained aphanitic matrix; 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 Earth's surface. It is often found in oceanic crust and volcanic regions.
Uses & applications
Basalt is used extensively in construction for aggregate, road base, railroad ballast, and high-quality concrete. This specific specimen is of interest for educational and mineral collecting.
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 its heavy weight (high density), dark color, and fine-grained texture. Look for small glassy green grains which are olivine crystals. It is ubiquitous in volcanic arcs and mid-ocean ridges.
