igneous
Porphyritic Basalt
Basalt with Feldspar phenocrysts
Hardness: 6.0; Color: Dark grey to black groundmass with orange/white phenocrysts; Luster: Dull/Sub-metallic; Crystal Structure: Aphanitic (fine-grained) with larger embedded crystals; Cleavage: None/Conchoidal.
- Hardness
- 6
- Color
- Dark grey to black groundmass with orange/white phenocrysts
- Luster
- Dull/Sub-metallic
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Physical properties
Hardness: 6.0; Color: Dark grey to black groundmass with orange/white phenocrysts; Luster: Dull/Sub-metallic; Crystal Structure: Aphanitic (fine-grained) with larger embedded crystals; Cleavage: None/Conchoidal.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface, typically in volcanic regions. The large crystals (phenocrysts) formed earlier in the cooling process deep underground.
Uses & applications
Commonly used as crushed stone for road construction, concrete aggregate, railroad ballast, and occasionally as decorative garden stones or river rocks.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. The orange spots in this specimen are likely weathered feldspar or olivine crystals.
Field identification & locations
Look for a dense, dark, heavy rock with visible distinct crystal inclusions ('spots') of a different color. Common in volcanic terrains, riverbeds, and glacial till.
