igneous
Basalt with Porphyritic Texture
Porphyritic Basalt
Hardness: 6 (Mohs scale); Color: Dark grey to black matrix with lighter phenocrysts; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained) matrix with visible large crystals; Specific gravity: 2.8-3.0.
- Hardness
- 6 (Mohs scale)
- Color
- Dark grey to black matrix with lighter phenocrysts
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6 (Mohs scale); Color: Dark grey to black matrix with lighter phenocrysts; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained) matrix with visible large 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 Earth's surface. The large visible crystals (phenocrysts) formed slowly underground before the eruption.
Uses & applications
Used primarily in construction (crushed stone, road base), as a decorative stone in landscaping, and occasionally as a source of industrial minerals.
Geological facts
Basalt is the most common rock 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, dark color, and fine-grained texture with larger embedded crystals. Commonly found in volcanic regions, riverbeds, and as glacial till.
