igneous

Basalt

Hardness: 6.0; Color: Dark grey to black, often weathering to brown; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained) to porphyritic; Specific Gravity: 2.8–3.0

Hardness: 6
Color: Dark grey to black, often weathering to brown
Luster: Dull to sub-metallic

Identified May 24, 2026More igneous →

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Physical properties

Hardness: 6.0; Color: Dark grey to black, often weathering to brown; Luster: Dull to sub-metallic; 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 a moon. It is the most common rock in Earth's crust (oceanic crust).

Uses & applications

Extensively used in construction for aggregate, road base, railroad ballast, and high-quality asphalt. It is also used as a dimension stone for floor tiles and monuments.

Geological facts

Basalt makes up most of the ocean floors on Earth. It is also widespread on the Moon and Mars. Many famous formations like the Giant's Causeway in Ireland are made of columnar basalt.

Field identification & locations

Identify by its dark color, heavy weight (relative to size), and fine-grained texture. It often features small holes called vesicles. Commonly found in volcanic regions and coastal areas.

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