igneous
Basalt with Olivine Phenocrysts
Extrusive Igneous Rock (Mafic)
Hardness: 6 on Mohs scale; Color: Dark gray to black with greenish olivine crystals; Luster: Dull to sub-vitreous; Crystal Structure: Aphanitic (fine-grained) groundmass with phaneritic phenocrysts; Specific Gravity: 2.8 - 3.0
- Hardness
- 6 on Mohs scale
- Color
- Dark gray to black with greenish olivine crystals
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6 on Mohs scale; Color: Dark gray to black with greenish olivine crystals; Luster: Dull to sub-vitreous; Crystal Structure: Aphanitic (fine-grained) groundmass with phaneritic phenocrysts; Specific Gravity: 2.8 - 3.0
Formation & geological history
Formed from the rapid cooling of low-viscosity, iron- and magnesium-rich lava flows at or near the Earth's surface. Geological age varies widely depending on the specific volcanic province.
Uses & applications
Used in construction, aggregate for roads, railroad ballast, and sometimes cut into decorative stones or monuments.
Geological facts
Basalt is the most common rock type in the Earth's crust underlying the world's ocean basins, and it is also found extensively on the Moon and Mars.
Field identification & locations
Identify by its dark, fine-grained matrix and heavy feel relative to its size. Commonly found in volcanic regions, oceanic islands, and flood basalt provinces like the Columbia River Plateau.
