igneous

Basalt (Polished)

Extrusive mafic igneous rock

Hardness: 6 (Mohs scale), Color: Dark grey to black, Luster: Dull to sub-vitreous when polished, Structure: Aphanitic (fine-grained), Specific Gravity: 2.8–3.0

Identified February 28, 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-vitreous when polished, Structure: Aphanitic (fine-grained), Specific Gravity: 2.8–3.0

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava at the Earth's surface. Basalt is the most common rock type in the Earth's crust (oceanic plates).

Uses & applications

Commonly used in construction as aggregate, for paving, and as railroad ballast. Polished specimens are used for decoration, massage stones, and aquarium landscaping.

Geological facts

Basalt is found on other planetary bodies like the Moon, Mars, and Venus. It makes up most of the ocean floors and is the primary rock of the Hawaiian Islands.

Field identification & locations

Identify in the field by its dark color, heavy weight, and lack of visible crystals. Commonly found in volcanic outcrops or as water-worn pebbles in rivers draining volcanic areas.

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