igneous
Basalt (River Worn)
Mafic Igneous Rock (primarily Plagioclase and Pyroxene)
Hardness: 6-7 Mohs; Color: Dark grey to greenish-black; Luster: Dull/Earthy (weathered); Crystal Structure: Aphanitic (fine-grained); Specific Gravity: 2.8-3.0.
- Hardness
- 6-7 Mohs
- Color
- Dark grey to greenish-black
- Luster
- Dull/Earthy (weathered)
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Physical properties
Hardness: 6-7 Mohs; Color: Dark grey to greenish-black; Luster: Dull/Earthy (weathered); Crystal Structure: Aphanitic (fine-grained); 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. This specific specimen shows rounding and smoothing from fluvial (river) erosion.
Uses & applications
Commonly used as crushed stone for construction, road base, railroad ballast, and sometimes polished for decorative garden stones or massage stones.
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 extensively on the Moon and Mars.
Field identification & locations
Identify by its dark color, heavy weight (density), and fine-grained texture. Commonly found in volcanic regions or in riverbeds downstream from volcanic plateaus.
