igneous

Basalt

Basalt (Mafic Extrusive)

Hardness (Mohs): 6; Color: Dark gray to black; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained) to porphyritic; Specific Gravity: 2.8 - 3.1

Color: Dark gray to black
Luster: Dull to sub-metallic

Identified April 8, 2026More igneous →

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Physical properties

Hardness (Mohs): 6; Color: Dark gray to black; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained) to porphyritic; Specific Gravity: 2.8 - 3.1

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. Common in oceanic crust and mid-ocean ridges.

Uses & applications

Extensively used in construction for road base, concrete aggregate, and railroad ballast. Also used as dimension stone for tiles and monuments.

Geological facts

Basalt is the most common volcanic rock on Earth. It also covers large areas of the Moon (the Lunar Maria) and Mars.

Field identification & locations

Identify by its dark color, heavy weight (relative to size), and fine-grained texture. It often shows smooth, water-worn surfaces if found in riverbeds like the specimen pictured.

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