igneous
Basalt (Weathered Pebble)
Basalt (Mafic Extrusive Igneous Rock)
Hardness: 5-6 Mohs; Color: Gray to dark gray/charcoal; Luster: Dull or earthy when weathered; Crystal Structure: Aphanitic (fine-grained); Specific Gravity: 2.8-3.0
- Hardness
- 5-6 Mohs
- Color
- Gray to dark gray/charcoal
- Luster
- Dull or earthy when weathered
Identified More igneous →
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Physical properties
Hardness: 5-6 Mohs; Color: Gray to dark gray/charcoal; Luster: Dull or earthy when 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 near the Earth's surface. This specimen shows water-worn rounding, suggesting origin from a riverbed or coastal environment.
Uses & applications
Crushed basalt is used in construction for road base, concrete aggregate, and railroad ballast. In slab form, it is used for floor tiles and monuments.
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 for its size, and absence of visible large crystals. Most common in volcanic regions or as gravel in glacial deposits.
