igneous

Basalt

Hardness: 6 (Mohs scale). Color: Dark gray to black, often weathering to greenish or brown. Luster: Dull to sub-metallic. Crystal structure: Aphanitic (fine-grained), sometimes vesicular or porphyritic. Specific gravity: 2.8 - 3.0. Composition: Plagioclase feldspar and pyroxene.

Hardness: 6 (Mohs scale)
Color: Dark gray to black, often weathering to greenish or brown
Luster: Dull to sub-metallic

Identified May 25, 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

Basalt is an extrusive volcanic rock 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. It is the most common rock type in Earth's crust.

Uses & applications

Extensively used in construction for aggregate, road base, concrete, and railroad ballast. Historically used in sculpting and as a decorative stone. Crushed basalt is even used for carbon sequestration experiments.

Geological facts

Basalt makes up most of the ocean floor and is also prevalent on Mars and the Moon (the dark lunar maria are basaltic lava flows). It is the most common rock on Earth's surface.

Field identification & locations

Identify by its heavy weight (density), fine-grained texture, and dark color. It often forms hexagonal pillars known as columnar jointing in large flows. Found globally in volcanic regions and oceanic crust.

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