igneous

Basalt with Iron Oxidation

Mafic Igneous Rock (primarily Plagioclase and Pyroxene)

Hardness: 6 (Mohs scale); Color: Dark grey to black with reddish-brown oxidation crust; Luster: Dull to earthy; Crystal Structure: Aphanitic (fine-grained); Specific Gravity: 2.8 - 3.0

Hardness: 6 (Mohs scale)
Color: Dark grey to black with reddish-brown oxidation crust
Luster: Dull to earthy

Identified April 5, 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 with reddish-brown oxidation crust; Luster: Dull to earthy; Crystal 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 or very near the Earth's surface. It can be found in oceanic crust, volcanic islands, and continental flood basalts.

Uses & applications

Used extensively in construction as an aggregate for road base, concrete, and railroad ballast. Fine-grained specimens are also used for stone carving and as thermal insulators.

Geological facts

Basalt is the most common rock type in the Earth's crust and also covers large areas of the Moon (the Lunar Maria), Mars, and Venus.

Field identification & locations

Identify by its dark color, heavy weight (relative to size), and fine-grained texture. Reddish staining indicates weathering or iron content. Commonly found in volcanic regions or as rounded river cobbles.

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