igneous

Basalt River Stone (Tumbled)

Basalt (Mafic Extrusive Igneous Rock)

Hardness: 6-7 on Mohs scale. Color: Dark grey to black, often weathering to greyish-white on higher surfaces. Luster: Dull to sub-metallic. Crystal structure: Aphanitic (fine-grained) to porphyritic. Specific gravity: 2.8-3.0.

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

Identified March 14, 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 specimen has been Rounded and smoothed by fluvial (river) or glacial abrasion over thousands of years.

Uses & applications

Extensively used in construction as aggregate for concrete and asphalt, railroad ballast, and stone dust. Tumbled specimens are popular in spa treatments (hot stone massage) and 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. It covers roughly 70% of Earth's surface.

Field identification & locations

Identify in the field by its dark color, heavy weight (density), and fine-grained texture. It will not react with acid. Commonly found in volcanic fields, riverbeds, and coastal regions.

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