igneous

Basalt

Basalt (Mafic volcanic rock)

Hardness: 6-7 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained) to porphyritic; Specific Gravity: 2.8–3.0.

Hardness: 6-7 on Mohs scale
Color: Dark grey to black
Luster: Dull to sub-metallic

Identified May 12, 2026More igneous →

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Physical properties

Hardness: 6-7 on Mohs scale; Color: Dark grey to black; 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, primarily making up the ocean floors.

Uses & applications

Extensively used in construction for aggregate, road base, railroad ballast, and concrete. Also used as a dimension stone for flooring and monuments. High-quality samples are used for stone carving and as thermal insulation (rock wool).

Geological facts

Basalt is equivalent to the composition of Earth's mantle and is extremely common on the Moon, Mars, and Venus. The famous Giant's Causeway in Northern Ireland is made of columnar basalt.

Field identification & locations

Identified in the field by its dark color, heavy weight (density), and fine-grained texture. It often shows vesicles (gas bubbles) or phenocrysts. Commonly found in volcanic regions, oceanic islands, and mid-ocean ridges.

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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