igneous

Basalt

Extrusive mafic igneous rock

Hardness: 5-6 (Mohs); Color: Dark gray to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Cleavage: None/conchoidal fracture; Specific gravity: 2.8–3.0

Hardness: 5-6 (Mohs)
Color: Dark gray to black
Luster: Dull to sub-metallic

Identified April 6, 2026More igneous →

Identify your own rocks.

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

App Store Google Play

Physical properties

Hardness: 5-6 (Mohs); Color: Dark gray to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Cleavage: None/conchoidal fracture; 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 a moon. Basalt comprises more than 90% of all volcanic rock on Earth.

Uses & applications

Extensively used in construction, especially as crushed stone for road base, concrete aggregate, railroad ballast, and asphalt pavement. Finer grades are used for rock wool insulation.

Geological facts

Basalt is the most common rock type in the Earth's crust as it makes up most of the ocean floor. Large areas of the Moon's surface, the lunar maria, are also composed of basaltic lava flows.

Field identification & locations

Identify by its dark color, heavy weight (density), and lack of visible crystals to the naked eye. It is found globally in volcanic regions such as the Pacific Northwest of the USA, Iceland, and Hawaii.

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