igneous

Basalt

Extrusive mafic igneous rock

Hardness: 6 (Mohs scale), Color: Dark grey to charcoal, Luster: Dull/Matte, Crystal structure: Aphanitic (fine-grained), Cleavage: None/Irregular, Specific gravity: 2.8 - 3.0

Identified April 11, 2026More igneous →

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Physical properties

Hardness: 6 (Mohs scale), Color: Dark grey to charcoal, Luster: Dull/Matte, Crystal structure: Aphanitic (fine-grained), Cleavage: None/Irregular, 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. This specific specimen shows signs of mechanical weathering and rounding by water.

Uses & applications

Used primarily in construction for road base, aggregate, and concrete. Also used for high-tensile mineral wool insulation and architectural stone.

Geological facts

Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. Large-scale cooling of basalt often forms unique hexagonal columns, such as at the Giant's Causeway.

Field identification & locations

Identify in the field by its dark color, heavy weight (relative to size), and very fine-grained texture that lacks visible crystals. Commonly found in coastal areas, riverbeds near volcanic ranges, and ocean basins.

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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