igneous

Basalt River Pebble

Basalt

Hardness: 6 on Mohs scale. Color: Dark grey to black. Luster: Dull or earthy. Crystal structure: Aphanitic (fine-grained), typically too small to see with the naked eye. Specific gravity: 2.8–3.0.

Hardness: 6 on Mohs scale
Color: Dark grey to black
Luster: Dull or earthy

Identified May 28, 2026More igneous →

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Physical properties

Hardness: 6 on Mohs scale. Color: Dark grey to black. Luster: Dull or earthy. Crystal structure: Aphanitic (fine-grained), typically too small to see with the naked eye. 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 specific specimen is a water-worn river pebble, shaped by mechanical weathering in a fluvial environment.

Uses & applications

Basalt is used extensively in construction for aggregate, road base, and railroad ballast. Fine-grained pebbles like this are sometimes used in aquarium decor or landscaping.

Geological facts

Basalt is the most common rock type in the Earth's crust and makes up the majority 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 for its size, and lack of visible crystals. It is commonly found in volcanic regions or in riverbeds downstream from volcanic outcrops.

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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