igneous

Basalt Beach Pebble

Basalt (Aphanitic Mafic Igneous Rock)

Hardness: 6 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Microcrystalline (aphanitic); Specific gravity: 2.8–3.0. This specimen shows a smooth, water-worn texture.

Hardness: 6 on Mohs scale
Color: Dark grey to black
Luster: Dull to sub-metallic

Identified May 10, 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. This specific pebble was subsequently shaped and polished by wave action in a high-energy coastal environment.

Uses & applications

Commonly used as decorative garden stones, in massage therapy (hot stones), and as aggregate in construction when found in large quantities.

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 on the Moon and Mars.

Field identification & locations

Identified by its dark color, heavy weight for its size, and absence of visible large crystals. Commonly found on volcanic coastlines like those in Iceland, Hawaii, or the Pacific Northwest.

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