igneous

Basalt (River Stone)

Basalt

Hardness: 6-7 Mohs; Color: dark grey to black; Luster: dull/matte; Crystal structure: aphanitic (fine-grained); Specific Gravity: 2.8–3.0. This specimen shows a rounded, water-worn texture.

Hardness: 6-7 Mohs
Color: dark grey to black
Luster: dull/matte

Identified May 28, 2026More igneous →

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Physical properties

Hardness: 6-7 Mohs; Color: dark grey to black; Luster: dull/matte; Crystal structure: aphanitic (fine-grained); Specific Gravity: 2.8–3.0. This specimen shows a rounded, water-worn texture.

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. The rounded shape indicates erosion in a high-energy aquatic environment such as a river or beach.

Uses & applications

Commonly used in construction as aggregate, for road base, concrete, and railroad ballast. Smooth river-worn basalt is often used in landscaping and massage therapy.

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 high density, dark color, and fine-grained texture. Found globally in volcanic regions and riverbeds downstream from volcanic sources.

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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