igneous
Basalt (with Porphyritic Texture)
Basalt
Hardness: 6-7 (Mohs); Color: Dark gray to black with white plagioclase phenocrysts; Luster: Dull to sub-vitreous; Structure: Aphanitic to porphyritic; Specific Gravity: 2.8–3.0
- Hardness
- 6-7 (Mohs)
- Color
- Dark gray to black with white plagioclase phenocrysts
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6-7 (Mohs); Color: Dark gray to black with white plagioclase phenocrysts; Luster: Dull to sub-vitreous; Structure: Aphanitic to porphyritic; 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. Often found in oceanic crust and volcanic regions.
Uses & applications
Crushed stone for road base, concrete aggregate, railroad ballast, and occasionally used in polished form for decorative landscaping or massage stones.
Geological facts
Basalt is the most common rock type in the Earth's crust and also makes up most of the surface of the Moon and Mars.
Field identification & locations
Identify by its dark, dense appearance and small visible crystals (phenocrysts). Commonly found on beaches near volcanic areas or in riverbeds. Collectors look for unique porphyritic patterns.
