igneous
Basalt (Beach Pebble)
Extrusive mafic igneous rock
Hardness: 5-6 (Mohs); Color: Dark grey to black; Luster: Dull/Matte; Structure: Fine-grained (aphanitic) or glassy; Cleavage: None; Specific Gravity: 2.8–3.0
- Hardness
- 5-6 (Mohs)
- Color
- Dark grey to black
- Luster
- Dull/Matte
Identified More igneous →
Explore Basalt (Beach Pebble) in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 5-6 (Mohs); Color: Dark grey to black; Luster: Dull/Matte; Structure: Fine-grained (aphanitic) or glassy; Cleavage: None; Specific Gravity: 2.8–3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. This specific specimen appears to be water-worn, indicating it was shaped by fluvial or coastal erosion over centuries.
Uses & applications
Commonly used as aggregate in construction, road base, and decorative landscaping. Smooth pebbles are often used in hot stone massage or as 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 in the field by its dark color, heavy weight for its size, and lack of visible crystals. It is ubiquitous along volcanic coastlines and riverbeds in tectonic regions.
