igneous

Basalt

Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Cleavage: None; Specific gravity: 2.8–3.0

Hardness: 6 (Mohs scale)
Color: Dark grey to black
Luster: Dull to sub-metallic

Identified April 11, 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; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Cleavage: None; Specific gravity: 2.8–3.0

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava (basaltic lava) exposed at or very near the surface of a terrestrial planet or a moon. Most common rock in the Earth's crust.

Uses & applications

Commonly used in construction as aggregate for concrete and road base, floor tiles, and in monuments.

Geological facts

Basalt also exists on other planetary bodies; much of the Moon's surface 'Maria' are plains of basaltic lava flows. It is the most common volcanic rock on Earth.

Field identification & locations

Identify in the field by its dark color, heavy weight (relative to size), and very fine-grained texture. It often shows vesicular (bubbly) textures if gases were trapped during cooling.

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