igneous

Basalt

Mafic Igneous Rock (primarily Plagioclase Feldspar and Pyroxene)

Hardness: 6 (Mohs scale); Color: Black to dark grey; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained) to porphyritic; Cleavage: None (conchoidal fracture); Specific Gravity: 2.8–3.0

Hardness: 6 (Mohs scale)
Color: Black to dark grey
Luster: Dull to sub-metallic

Identified January 12, 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 (mafic lava) at or very near the Earth's surface. Most commonly formed at mid-ocean ridges and hotspots.

Uses & applications

Extensively used in construction as crushed stone for road base, railroad ballast, and concrete aggregate. High-quality specimens are used for 'hot stone' massage therapy and as decorative landscaping stones.

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 found in abundance on the Moon and Mars.

Field identification & locations

Identify by its dark color, heavy weight (relative to size), and fine-grained texture. Commonly found in volcanic regions, riverbeds near volcanic flows, and along coastlines. It often shows 'vesicles' (gas bubbles) or a smooth, water-worn appearance 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