igneous

Basalt

Hardness: 6 on Mohs scale; Color: Dark grey to black, weathering to brown; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained) to porphyritic; Density: 2.9-3.1 g/cm³

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

Identified May 25, 2026More igneous →

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Physical properties

Hardness: 6 on Mohs scale; Color: Dark grey to black, weathering to brown; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained) to porphyritic; Density: 2.9-3.1 g/cm³

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 volcanic rock on Earth.

Uses & applications

Extensively used in construction, especially as crushed stone for road base, concrete aggregate, and railroad ballast. Also used as a dimension stone for flooring and monuments.

Geological facts

Basalt makes up most of the world's ocean floor. It is also found on the Moon and Mars, where the dark 'maria' (seas) are ancient basaltic lava flows.

Field identification & locations

Identified in the field by its dark color, heavy weight, and fine-grained texture. It often shows vesiculation (small holes from gas bubbles) or columnar jointing. Commonly found in volcanic island chains and oceanic crust.

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