igneous

Basalt

Hardness: 6 (Mohs scale); Color: Dark grey to black, often weathering to brown; Luster: Dull/earthy; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8 - 3.0

Hardness: 6 (Mohs scale)
Color: Dark grey to black, often weathering to brown
Luster: Dull/earthy

Identified April 12, 2026More igneous →

Identify your own rocks.

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

App Store Google Play

Physical properties

Hardness: 6 (Mohs scale); Color: Dark grey to black, often weathering to brown; Luster: Dull/earthy; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8 - 3.0

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava exposed at or very near the surface of a terrestrial planet or moon. Most oceanic crust is composed of basalt.

Uses & applications

Extensively used in construction for aggregate, road base, railroad ballast, and high-quality concrete. Also used for pavers and as a component in stonewash applications for textiles.

Geological facts

Basalt is the most common volcanic rock on Earth and also makes up much of the surface of the Moon, Venus, and Mars.

Field identification & locations

Identify by its dark color, heavy weight (relative to size), and fine-grained texture with no visible crystals to the naked eye. Often found in volcanic regions or riverbeds near volcanic flows.

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