igneous

Basalt

Basalt (Mafic volcanic rock)

Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull or submetallic; Crystal structure: Aphanitic (fine-grained) to porphyritic; Specific gravity: 2.8–3.0

Hardness: 6 (Mohs scale)
Color: Dark grey to black
Luster: Dull or submetallic

Identified April 3, 2026More igneous →

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Physical properties

Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull or submetallic; Crystal structure: Aphanitic (fine-grained) to porphyritic; Specific gravity: 2.8–3.0

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava exposed at or very near the surface of a terrestrial planet or moon. Basalt is the most common rock type on Earth's crust.

Uses & applications

Extensively used in construction for road base, concrete aggregate, railroad ballast, and dimension stone for paving and flooring. It is also used as an industrial fiber (basalt fiber).

Geological facts

Most of the ocean floor is composed of basalt. It is also common on other planetary bodies like the Moon, Mars, and Venus. The Giant's Causeway in Northern Ireland is a famous example of columnar basalt.

Field identification & locations

Identify in the field by its dark color, heavy weight (relative to size), and fine-grained texture. It often shows vesicles (gas bubbles) or phenocrysts. Found in volcanic regions and oceanic crustal outcrops.

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