igneous

Basalt

Basalt (Mafic volcanic rock)

Hardness: 6-7 Mohs; Color: dark grey to black; Luster: dull to sub-metallic; Crystal structure: fine-grained (aphanitic) or porphyritic; Specific gravity: 2.8 to 3.0. Dense and heavy for its size.

Hardness: 6-7 Mohs
Color: dark grey to black
Luster: dull to sub-metallic

Identified March 13, 2026More igneous →

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Physical properties

Hardness: 6-7 Mohs; Color: dark grey to black; Luster: dull to sub-metallic; Crystal structure: fine-grained (aphanitic) or porphyritic; Specific gravity: 2.8 to 3.0. Dense and heavy for its size.

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 in Earth's crust, primarily forming the ocean floor.

Uses & applications

Extensively used in construction for aggregate, road base, and railroad ballast. In industry, it can be melted into stone wool for insulation. High-density specimens are used for river stone massage and landscaping decoration.

Geological facts

Basalt is the most common rock type on the surfaces of Mars and the Moon (Lunar Maria). It famously forms unique hexagonal columns at the Giant's Causeway in Ireland and Devil's Postpile in California.

Field identification & locations

Identify in the field by its dark, uniform color, fine grain, and heaviness. It often has small 'vesicles' (bubbles) from trapped gas. Commonly found in volcanic regions and ocean shorelines.

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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