igneous

Basalt

Hardness: 6.0; Color: Dark grey to black; Luster: Dull/Matte; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8-3.0

Hardness: 6
Color: Dark grey to black
Luster: Dull/Matte

Identified May 12, 2026More igneous →

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Physical properties

Hardness: 6.0; Color: Dark grey to black; Luster: Dull/Matte; Crystal structure: Aphanitic (fine-grained); 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. This specimen appears to be a water-worn river stone.

Uses & applications

Used primarily in construction for aggregate, road base, and railroad ballast. Fine-grained specimens are also used for stone massage and decorative landscaping.

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 lack of visible crystals to the naked eye. Often found in volcanic regions or as rounded pebbles in riverbeds.

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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