igneous

Basalt with Iron Oxide staining

Mafic Igneous Rock (primarily Plagioclase and Pyroxene)

Hardness: 6.0; Color: Dark grey to black with reddish-brown oxidation; Luster: Dull to earthy; Structure: Fine-grained (aphanitic); Cleavage: None; Specific Gravity: 2.8-3.0.

Hardness: 6
Color: Dark grey to black with reddish-brown oxidation
Luster: Dull to earthy

Identified May 26, 2026More igneous →

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Physical properties

Hardness: 6.0; Color: Dark grey to black with reddish-brown oxidation; Luster: Dull to earthy; Structure: Fine-grained (aphanitic); Cleavage: None; 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 orange-brown spots are due to the oxidation of iron minerals (weathering).

Uses & applications

Commonly used as aggregate in construction (roads/concrete), industrial stone, and occasionally for basalt fiber or 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 common on the Moon and Mars.

Field identification & locations

Identify by its heavy weight relative to size, dark color, and lack of visible crystals. Commonly found in volcanic regions or as river stones.

Other igneous specimens

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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