igneous

Basalt (River Stone)

Extrusive mafic igneous rock

Hardness: 6-7 on Mohs scale; Color: Dark grey to blackish-brown; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8-3.0

Hardness: 6-7 on Mohs scale
Color: Dark grey to blackish-brown
Luster: Dull to sub-metallic

Identified May 25, 2026More igneous →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Hardness: 6-7 on Mohs scale; Color: Dark grey to blackish-brown; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8-3.0

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth surface. This specimen appears water-worn, suggesting a secondary transport via fluvial (river) environments.

Uses & applications

Crushed stone for road base, concrete aggregate, railroad ballast, and decorative landscaping or river rock gardens.

Geological facts

Basalt is the most common rock type in the Earth's crust and also makes up most of the ocean floor. It is found on the Moon and Mars as well.

Field identification & locations

Identify in the field by its heavy weight (density), dark color, and lack of visible crystals. Commonly found in volcanic regions or in riverbeds downstream from volcanic sources.

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