igneous

Weathered Basalt with Iron Staining

Mafic Igneous Rock

Hardness: 5-6 (Mohs); Color: Dark grey to charcoal with reddish-tan iron oxide weathering; Luster: Dull/Earthy; Crystal Structure: Aphanitic (fine-grained); Specific Gravity: 2.8-3.0

Hardness: 5-6 (Mohs)
Color: Dark grey to charcoal with reddish-tan iron oxide weathering
Luster: Dull/Earthy

Identified May 31, 2026More igneous →

Identify your own rocks.

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

App Store Google Play

Physical properties

Hardness: 5-6 (Mohs); Color: Dark grey to charcoal with reddish-tan iron oxide weathering; Luster: Dull/Earthy; 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's surface. The visible reddish-brown surface layer is due to chemical weathering (oxidation) of iron-bearing minerals like olivine or pyroxene.

Uses & applications

Commonly used as crushed stone for road base, concrete aggregate, railroad ballast, and high-quality asphalt pavement.

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 extensively on the Moon and Mars.

Field identification & locations

Identify by its heavy weight (high density), dark interior color, and lack of visible crystals. It can be found in volcanic fields, riverbeds, and glacial deposits. This specimen shows 'rind' weathering where the exterior differs in color from the fresh interior rock.

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

Dalmatian Jasper

Aplite with Arfvedsonite inclusions

igneous

Magnetite

Iron(II,III) oxide (Fe3O4)

mineral

Blue Apatite

Apatite (Group), Ca5(PO4)3(F,Cl,OH)

mineral

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral