igneous

Basalt

Mafic volcanic rock (Basalt)

Hardness: 6-7 on Mohs scale; Color: dark grey to black; Luster: dull to earthy; Crystal structure: fine-grained (aphanitic) or porphyritic; Cleavage: none; Specific gravity: 2.8–3.0

Hardness: 6-7 on Mohs scale
Color: dark grey to black
Luster: dull to earthy

Identified May 3, 2026More igneous →

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Physical properties

Hardness: 6-7 on Mohs scale; Color: dark grey to black; Luster: dull to earthy; Crystal structure: fine-grained (aphanitic) or porphyritic; Cleavage: none; Specific gravity: 2.8–3.0

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. This particular specimen shows rounding due to fluvial (river) or glacial transport.

Uses & applications

Major use in construction as crushed stone for road base, railroad ballast, and concrete aggregate. Also used for high-quality floor tiles and stone monuments.

Geological facts

Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. It is also found on the Moon, Mars, and Venus.

Field identification & locations

Identify in the field by its dark color, heavy weight (density), and fine-grained texture. It often weathers to a reddish-brown color due to iron oxidation. Very common in volcanic regions and riverbeds draining those 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