igneous
Basalt (Weathered/Tumbled)
Extrusive Mafic Igneous Rock
Hardness: 6 (Mohs scale); Color: Dark gray to greenish-gray; Luster: Dull to earthy; Crystal Structure: Aphanitic (fine-grained); Specific Gravity: 2.8 - 3.0
- Hardness
- 6 (Mohs scale)
- Color
- Dark gray to greenish-gray
- Luster
- Dull to earthy
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Physical properties
Hardness: 6 (Mohs scale); Color: Dark gray to greenish-gray; Luster: Dull to earthy; 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 specimen appears to have been physically weathered, likely by water or glacial transport, rounding its edges.
Uses & applications
Commonly used in construction (aggregate), paving, and landscaping. High-quality dense basalt is also used for dimensional stone and floor tiles.
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 extremely common on the Moon and Mars.
Field identification & locations
Identify in the field by its dark color, fine-grained texture (individual crystals are usually too small to see with the naked eye), and heavy weight for its size. It often contains vesicles (small holes) though this specimen is solid.
