igneous
Basalt River Pebble
Aphanitic Mafic Igneous Rock
Hardness: 6 (Mohs); Color: Dark grey to charcoal; Luster: Dull to earthy; Crystal structure: Fine-grained (aphanitic); Specific gravity: 2.8-3.0
- Hardness
- 6 (Mohs)
- Color
- Dark grey to charcoal
- Luster
- Dull to earthy
Identified More igneous →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 6 (Mohs); Color: Dark grey to charcoal; Luster: Dull to earthy; Crystal structure: Fine-grained (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 specimen has been rounded by fluvial (river) erosion over many years.
Uses & applications
Basalt is used in construction as aggregate, road base, and railroad ballast. Smooth river pebbles are used in landscaping and decorative masonry.
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 dark color, heavy weight for its size, and lack of visible large crystals. Commonly found in riverbeds, glacial tills, and volcanic regions.
