igneous
Basalt (River Pebble)
Basalt
Hardness: 6-7 on Mohs scale; Color: Dark grey to black, greenish-grey; Luster: Dull to satin when wet; Texture: Fine-grained (aphanitic), rounded and smoothed by water erosion; Specific Gravity: ~2.8-3.0
- Hardness
- 6-7 on Mohs scale
- Color
- Dark grey to black, greenish-grey
- Luster
- Dull to satin when wet
Identified More igneous →
Explore Basalt (River Pebble) in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 6-7 on Mohs scale; Color: Dark grey to black, greenish-grey; Luster: Dull to satin when wet; Texture: Fine-grained (aphanitic), rounded and smoothed by water erosion; 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. Rounded shape acquired through mechanical weathering and stream or beach transportation.
Uses & applications
Crushed stone for construction, aggregate in concrete, road base, landscaping rock, and general stone collecting.
Geological facts
Basalt is the most common rock type in the Earth's crust, making up most of the oceanic floor. It is also found in large amounts on the Moon and Mars.
Field identification & locations
Identify in the field by its dark color, heavy feel relative to size, fine-grained matrix, and rounded river-cobble shape. Extremely common in volcanic regions and riverbeds.
