igneous

Basalt

Basalt (Aphanitic Mafic Igneous Rock)

Hardness: 6.0 on Mohs scale; Color: Dark grey to black with brown weathering; Luster: Dull/earthy; Crystal structure: Fine-grained/aphanitic; Specific gravity: 2.8–3.0

Hardness: 6
Color: Dark grey to black with brown weathering
Luster: Dull/earthy

Identified May 31, 2026More igneous →

Identify your own rocks.

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

App Store Google Play

Physical properties

Hardness: 6.0 on Mohs scale; Color: Dark grey to black with brown weathering; Luster: Dull/earthy; 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 at or very near the Earth's surface. Common in oceanic crust and volcanic regions.

Uses & applications

Extensively used in construction as aggregate for road base, concrete, and railroad ballast. Also used as dimension stone for tiles and landscaping.

Geological facts

Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. It is also common on the Moon, Mars, and Venus.

Field identification & locations

Identify in the field by its dark color, heavy weight (relative to size), and fine-grained texture. Often shows signs of iron-oxide weathering (rusty spots).

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