igneous
Basalt River Stone
Aphanitic Mafic Igneous Rock (Basalt)
Hardness: 6-7 Mohs; Color: Dark grey to greenish-grey; Luster: Dull/Earthy; Crystal Structure: Fine-grained/Aphanitic; Specific Gravity: 2.8-3.0. This specimen shows a rounded, water-worn texture with some minor inclusion veins.
- Hardness
- 6-7 Mohs
- Color
- Dark grey to greenish-grey
- Luster
- Dull/Earthy
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Physical properties
Hardness: 6-7 Mohs; Color: Dark grey to greenish-grey; Luster: Dull/Earthy; Crystal Structure: Fine-grained/Aphanitic; Specific Gravity: 2.8-3.0. This specimen shows a rounded, water-worn texture with some minor inclusion veins.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. This particular specimen has been mechanically weathered and rounded by river or glacial transport over thousands of years.
Uses & applications
Commonly used in construction as aggregate, road base, and concrete. Smooth river stones are popular in landscaping, aquarium decor, and massage therapy.
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 on the Moon and Mars.
Field identification & locations
Identify by its heavy weight (high density), dark color, and fine-grained texture. Found globally in volcanic regions and riverbeds. For collectors, it is a standard example of an extrusive igneous rock.
