igneous

Basalt River Pebble

Basalt (fine-grained mafic igneous rock)

Hardness: 6 on Mohs scale; Color: Dark grey to charcoal; Luster: Dull/matte; Crystal Structure: Microcrystalline (aphanitic); Cleavage: None/conchoidal; Specific Gravity: 2.8-3.0.

Hardness: 6 on Mohs scale
Color: Dark grey to charcoal
Luster: Dull/matte

Identified March 24, 2026More igneous →

Identify your own rocks.

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

App Store Google Play

Physical properties

Hardness: 6 on Mohs scale; Color: Dark grey to charcoal; Luster: Dull/matte; Crystal Structure: Microcrystalline (aphanitic); Cleavage: None/conchoidal; Specific Gravity: 2.8-3.0.

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava at the earth's surface. This specimen has been water-worn and smoothed over thousands of years in a high-energy river or coastal environment.

Uses & applications

Used primarily as construction aggregate, road base, and in decorative landscaping. Polished stones are used in hot stone massage therapy and minor aquarium decor.

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 (lunar maria) and Mars.

Field identification & locations

Identify by its heavy weight (high density), dark color, and lack of visible crystals. It is commonly found in volcanic regions, riverbeds, and gravel pits.

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