igneous

Basalt (River Stone)

Basalt

Hardness: 6-7 on Mohs scale; Color: Dark grey to black, often with subtle banding when water-worn; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Cleavage: None (conchoidal fracture); Specific gravity: 2.8–3.0

Hardness: 6-7 on Mohs scale
Luster: Dull to sub-metallic

Identified May 16, 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 near the Earth's surface. This specific specimen has been smoothed by fluvial (river) or coastal water erosion over many years.

Uses & applications

Commonly used in construction as aggregate, in road base, for hot stone massage therapy due to heat retention, and in 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 found on the Moon and Mars.

Field identification & locations

Identify by its dark color, heavy weight for its size, and lack of visible crystals. Commonly found in volcanic regions, riverbeds, and beaches near basaltic cliffs. Collectors look for smooth, symmetrical shapes.

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