igneous

Basalt Pebble

Basalt

Hardness: 6 on Mohs scale. Color: Dark gray to black, often weathering to brownish tones. Luster: Dull or earthy. Structure: Fine-grained (Aphanitic) to microscopic. Cleavage: None. Specific Gravity: 2.8–3.0.

Hardness: 6 on Mohs scale
Color: Dark gray to black, often weathering to brownish tones
Luster: Dull or earthy

Identified May 26, 2026More igneous →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava at or near the Earth's surface. This specimen appears to be water-worn, indicating it was shaped by fluvial or coastal processes.

Uses & applications

Crushed basalt is used as aggregate in construction, road base, and railroad ballast. It is also used in cast basalt for abrasion-resistant liners and occasionally in stone 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, Mars, and Venus.

Field identification & locations

Identify in the field by its dark color, heavy weight (density), and fine-grained texture. It is often found in volcanic regions or as rounded pebbles in rivers and beaches.

Other igneous specimens

See all

Blue Apatite

Fluorapatite (Ca5(PO4)3F)

mineral

Dark Igneous Rock (Likely Basalt or Diabase)

Basalt (extrusive igneous rock) or Diabase (intrusive igneous rock - also known as Dolerite), largely composed of plagioclase feldspar, pyroxene (augite), and sometimes olivine and amphibole. Exact mineralogy would require thin section analysis.

Igneous