igneous

Basalt

Hardness (Mohs): 6; Color: dark grey to black; Luster: dull to velvety; Crystal structure: aphanitic (fine-grained); Specific gravity: 2.8-3.0; Cleavage: none.

Color: dark grey to black
Luster: dull to velvety

Identified May 28, 2026More igneous →

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Physical properties

Hardness (Mohs): 6; Color: dark grey to black; Luster: dull to velvety; Crystal structure: aphanitic (fine-grained); Specific gravity: 2.8-3.0; Cleavage: none.

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. Most common rock type in Earth's crust.

Uses & applications

Extensively used in construction for road base, concrete aggregate, asphalt pavement, and railroad ballast. Also used as dimension stone and in high-quality river stones for landscaping.

Geological facts

Basalt covers most of the ocean floor and is found on other planetary bodies like the Moon and Mars. It forms hexagonal columns when it cools slowly, such as at the Giant's Causeway.

Field identification & locations

Identify by its dark color, heavy weight (relative to size), and very fine-grained texture. It is commonly found in volcanic regions and ocean coastlines.

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