igneous
Basalt River Pebble
Basalt (Aphanitic Mafic Igneous Rock)
Hardness: 6; Color: Dark grey to charcoal; Luster: Dull/Earthy; Crystal Structure: Microcrystalline (Aphanitic); Specific Gravity: 2.8-3.0.
- Hardness
- 6
- Color
- Dark grey to charcoal
- Luster
- Dull/Earthy
Identified More igneous →
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Physical properties
Hardness: 6; Color: Dark grey to charcoal; Luster: Dull/Earthy; Crystal Structure: Microcrystalline (Aphanitic); 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 specific specimen has been rounded and smoothed by water erosion in a fluvial (river) environment.
Uses & applications
Large scale basalt is used in road base, concrete aggregate, and railroad ballast. Smooth pebbles are used in landscaping, massage therapy, and aquarium decor.
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 (density), and fine-grained texture. Commonly found in volcanic regions and riverbeds downstream from volcanic mountains.
