igneous
Basalt with Plagioclase Phenocrysts
Porphyritic Basalt
Hardness: 6-7 on Mohs scale. Color: Dark grey to black matrix with white or light-colored inclusions. Luster: Dull to sub-vitreous. Crystal structure: Aphanitic (fine-grained) matrix with visible macro-crystals (phenocrysts).
- Hardness
- 6-7 on Mohs scale
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Dark grey to black matrix with white or light-colored inclusions. Luster: Dull to sub-vitreous. Crystal structure: Aphanitic (fine-grained) matrix with visible macro-crystals (phenocrysts).
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or near the Earth's surface. The larger white crystals formed earlier within the cooling magma chamber before the final eruption.
Uses & applications
Used primarily in construction as aggregate for concrete and asphalt, road base, and railroad ballast. Exceptionally durable varieties are used for floor tiles and monuments.
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 in abundance on the Moon and Mars.
Field identification & locations
Identified by its dark, heavy, and fine-grained 'stony' matrix often containing distinct pinpoint or tabular lath-shaped white crystals. Common in volcanic regions and coastal areas near tectonic boundaries.
