igneous

Basalt (Vesicular or Porphyritic)

Basalt (composed primarily of plagioclase feldspar, pyroxene, and olivine)

Hardness: 6-7 on Mohs scale; Color: dark grey to black; Luster: dull to sub-metallic; Crystal structure: aphanitic (fine-grained) to porphyritic; Cleavage: none (conchoidal fracture); Specific gravity: 2.8-3.0.

Hardness: 6-7 on Mohs scale
Color: dark grey to black
Luster: dull to sub-metallic

Identified March 25, 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 the Earth's surface. It can be found in volcanic regions globally, often representing oceanic crust or continental flood basalts.

Uses & applications

Extensively used in construction as aggregate for roads and railroads, in concrete, and for stone masonry. It is also used in the production of rock wool (insulation) and occasionally used for decorative landscaping.

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 a primary component of the lunar maria on the Moon and much of the surface of Mars.

Field identification & locations

Identify in the field by its dark color, heavy weight (high density), and fine-grained texture. To collectors, specific textures like vesicular (holed) or porphyritic (having larger crystals embedded) are points of interest. Found on beaches near volcanic coastlines or in ancient volcanic fields.

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