Igneous
Basalt (with possible mineral veining)
Basalt (Aphanitic Mafic Igneous Rock)
Hardness: 6-7 (Mohs scale); Color: Dark grey to black, occasionally weathered to brown; Luster: Dull/Earthy; Crystal structure: Aphanitic (fine-grained); Cleavage: None; Specific Gravity: 2.8-3.0.
- Hardness
- 6-7 (Mohs scale)
- Color
- Dark grey to black, occasionally weathered to brown
- Luster
- Dull/Earthy
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Physical properties
Hardness: 6-7 (Mohs scale); Color: Dark grey to black, occasionally weathered to brown; Luster: Dull/Earthy; Crystal structure: Aphanitic (fine-grained); Cleavage: None; 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 specimen shows signs of fluvial or glacial rounding, indicating it was transported by water or ice over a long period.
Uses & applications
Commonly used as an aggregate in construction (road base, concrete, railroad ballast), for stone carvings, and occasionally in jewelry as or healing stones when polished.
Geological facts
Basalt is the most common rock type on 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 in the field by its dark color, heavy weight (density), and fine-grained texture. To distinguish from slate, check for a lack of foliation. Commonly found in volcanic fields, ocean basins, and riverbeds.
