igneous

Basalt

Basalt (Aphanitic Mafic Igneous Rock)

Hardness: 6 (Mohs scale); Color: Dark grey, black, or dark brown; Luster: Dull to sub-metallic; Structure: Fine-grained/aphanitic, often vesicular or columnar; Specific Gravity: 2.8–3.0

Hardness: 6 (Mohs scale)
Color: Dark grey, black, or dark brown
Luster: Dull to sub-metallic

Identified May 31, 2026More igneous →

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Physical properties

Hardness: 6 (Mohs scale); Color: Dark grey, black, or dark brown; Luster: Dull to sub-metallic; Structure: Fine-grained/aphanitic, often vesicular or columnar; 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 a moon. Most common rock type on Earth's crust.

Uses & applications

Extensively used in construction for aggregate, road base, railroad ballast, and ground-up for mineral wool insulation. Smaller polished pieces used in jewelry or decorative landscaping.

Geological facts

Basalt is the most common rock in Earth's crust and makes up most of the ocean floor. Large-scale basalt flows are known as 'traps', and the Giant's Causeway in Ireland is a famous example of columnar basalt.

Field identification & locations

Identify by its dark, heavy nature and lack of visible large crystals. Commonly found in volcanic regions, oceanic islands (like Hawaii), and mid-ocean ridges.

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