igneous

Basalt with Iron Oxides

Mafic Igneous Rock (Mafite)

Hardness: 6-7 Mohs; Color: Dark grey to black with reddish-brown oxidation; Luster: Dull to sub-metallic; Structure: Fine-grained (aphanitic) or vesicular; Specific gravity: 2.8–3.0.

Hardness: 6-7 Mohs
Color: Dark grey to black with reddish-brown oxidation
Luster: Dull to sub-metallic

Identified April 1, 2026More igneous →

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Physical properties

Hardness: 6-7 Mohs; Color: Dark grey to black with reddish-brown oxidation; Luster: Dull to sub-metallic; Structure: Fine-grained (aphanitic) or vesicular; 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 reddish spots indicate secondary oxidation (weathering) of iron minerals.

Uses & applications

Commonly used in construction as aggregate, road base, concrete, and railroad ballast. Occasionally used in stone masonry.

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 dark color, heavy weight (density), and fine-grained texture. Reddish staining indicates exposure to air and water which oxidizes the iron content.

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