igneous

Basalt

Basalt (Mafic volcanic rock)

Hardness: 5-6 (Mohs scale), Color: Dark grey to black, Luster: Dull/Matte, Crystal structure: Fine-grained/Aphanitic, Specific gravity: 2.8-3.0.

Identified April 13, 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 scale), Color: Dark grey to black, Luster: Dull/Matte, Crystal structure: Fine-grained/Aphanitic, Specific gravity: 2.8-3.0.

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava (magma) on or very near the Earth's surface. Most specimens are from the Cenozoic era, but can range across all geological ages.

Uses & applications

Used extensively in construction as road base, railroad ballast, and concrete aggregate. Also used for decorative stonework and in high-quality river stone landscaping.

Geological facts

Basalt is the most common rock type in the Earth's crust and makes up almost the entire ocean floor. It is also found frequently on the Moon and Mars.

Field identification & locations

Identify in the field by its heavy weight, dark color, and lack of visible crystals. Commonly found in coastal areas as smooth river/beach stones or in volcanic regions in columnar formations.

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