igneous
Basalt with olivine (Porphyritic Basalt)
Mafic Igneous Volcanic Rock (Extrusive Basalt)
Hardness: 6-6.5 on the Mohs scale; Color: Dark gray to black groundmass with light yellowish-green olivine or feldspar phenocrysts; Luster: Dull to sub-vitreous; Crystal structure: Aphanitic (fine-grained matrix) with porphyritic inclusions; Specific gravity: 2.8-3.0.
- Hardness
- 6-6
- Luster
- Dull to sub-vitreous
Identified More igneous →
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Physical properties
Hardness: 6-6.5 on the Mohs scale; Color: Dark gray to black groundmass with light yellowish-green olivine or feldspar phenocrysts; Luster: Dull to sub-vitreous; Crystal structure: Aphanitic (fine-grained matrix) with porphyritic inclusions; Specific gravity: 2.8-3.0.
Formation & geological history
Formed from the rapid cooling of mafic lava rich in magnesium and iron at or near the Earth's surface. Occurs commonly in oceanic crust, volcanic island arcs, and continental flood basalt provinces.
Uses & applications
Used widely in construction as crushed stone, concrete aggregate, railroad ballast, dimension stone, and basalt fiber production.
Geological facts
Basalt is the most common rock type in the Earth's crust, covering most of the ocean floors. It is also extremely common on the Moon and Mars.
Field identification & locations
Identified by its dark color, heavy weight for its size, fine grain, and presence of scattered pale greenish or whitish mineral phenocrysts. Commonly found along volcanic beaches, rivers, and volcanic fields.
