igneous

Basalt

Basalt (Mafic Extrusive)

Hardness: 6.0; Color: Dark grey to black; Luster: Dull/Sub-metallic; Crystal Structure: Aphanitic (fine-grained); Specific Gravity: 2.8 - 3.0

Hardness: 6
Color: Dark grey to black
Luster: Dull/Sub-metallic

Identified February 5, 2026More igneous →

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Physical properties

Hardness: 6.0; Color: Dark grey to black; Luster: Dull/Sub-metallic; Crystal Structure: Aphanitic (fine-grained); 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 on Earth's crust.

Uses & applications

Extensively used in construction for aggregate, road base, concrete, and railroad ballast. Also used in high-temp insulation (rock wool) and as decorative garden stone.

Geological facts

Basalt makes up most of the ocean floor on Earth and is also found on the Moon, Mars, and Venus. It often forms striking geometric columns like those at Giant's Causeway.

Field identification & locations

Identify in the field by its high density, dark color, and lack of visible crystals to the naked eye. Often weathered to a reddish-brown crust. Look for it in volcanic regions or riverbeds.

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