igneous

Basalt

Basalt (Phaneritic/Aphanitic Mafic Igneous Rock)

Hardness: 5–6 (Mohs scale); Color: Dark gray to black (often weathering to brown or rust-red); Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained) to porphyritic; Specific gravity: 2.8–3.0

Hardness: 5–6 (Mohs scale)
Color: Dark gray to black (often weathering to brown or rust-red)
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 magnesium-rich and iron-rich lava at or very near the Earth's surface. It is the most common rock type in the Earth's crust, primarily forming the ocean floors and large continental plateaus through volcanic eruptions.

Uses & applications

Extensively used in construction as crushed stone for road base, concrete aggregate, railroad ballast, and asphalt. High-quality dense basalt is sometimes used for floor tiles, monuments, and stone carvings.

Geological facts

Basalt covers more than 70% of the Earth's surface (mostly underwater). It is also found on other planetary bodies like the Moon (lunar maria), Mars, and Venus. Famous basalt structures include the Giant's Causeway in Northern Ireland and the Devils Postpile in California.

Field identification & locations

Identify in the field by its dark color, heavy weight (relative to size due to iron content), and lack of visible large crystals. It often breaks with a conchoidal or uneven fracture. Commonly found in volcanic regions, oceanic island chains (like Hawaii), and basaltic plateaus.

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

Blue Apatite

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

mineral

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral

Magnetite

Magnetite (Fe3O4)

mineral