Igneous

Basalt

Mafic volcanic rock (primarily plagioclase, pyroxene, and olivine)

Hardness: 6 (Mohs scale); Color: Dark grey to black, weathering to olive green or rusty brown; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained/microscopic); Cleavage: None; Specific Gravity: 2.9–3.1

Hardness: 6 (Mohs scale)
Color: Dark grey to black, weathering to olive green or rusty brown
Luster: Dull to sub-metallic

Identified March 21, 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

Formed from the rapid cooling of low-viscosity magnesium-rich and iron-rich lava. Most often found at mid-ocean ridges and hotspots. Geological age varies from modern volcanic flows to over 1 billion years old.

Uses & applications

Extensively used in construction as crushed aggregate for roads, concrete, and railroad ballast. Also used as dimension stone for tiles and historical monuments, and melted down to create rock wool insulation.

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 an extremely common rock on other planetary bodies like the Moon (lunar maria) and Mars.

Field identification & locations

Identify in the field by its dark color, heavy weight (relative to size), and fine-grained texture. It often weathers into a reddish or greenish exterior. Common in the Pacific Northwest (USA), Hawaii, and Iceland.

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

Magnetite

Iron(II,III) oxide (Fe3O4)

mineral

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral

Blue Apatite

Apatite (Group), Ca5(PO4)3(F,Cl,OH)

mineral

Magnetite

Magnetite (Fe3O4)

mineral