igneous

Basalt

Basalt (dominated by Plagioclase Feldspar and Pyroxene)

Hardness: 6; Color: dark grey to black; Luster: dull to earthy; Crystal structure: fine-grained (aphanitic), typically contains micro-crystals; Specific gravity: 2.8 - 3.0.

Hardness: 6
Color: dark grey to black
Luster: dull to earthy

Identified March 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; Color: dark grey to black; Luster: dull to earthy; Crystal structure: fine-grained (aphanitic), typically contains micro-crystals; Specific gravity: 2.8 - 3.0.

Formation & geological history

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. Most common rock on Earth's crust.

Uses & applications

Extensively used in construction for aggregate, road base, railroad ballast, and high-quality concrete. Sometimes used in sculpture or as polished tiles.

Geological facts

Basalt is the primary rock type making up the ocean floors and is also found extensively on the Moon and Mars. It can form unique hexagonal columns during cooling, known as columnar jointing.

Field identification & locations

Identify by its heavy weight (density), dark color, and very fine-grained texture. It often shows water-worn, dull surfaces when found as river or beach pebbles like this specimen.

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