igneous

Basalt (River Pebble)

Basalt

Hardness (Mohs scale): 6; Color: Dark grey to black; Luster: Dull or earthy; Crystal structure: Aphanitic (fine-grained); Cleavage: None/Irregular; Specific gravity: 2.8–3.0

Color: Dark grey to black
Luster: Dull or earthy

Identified May 14, 2026More igneous →

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Physical properties

Hardness (Mohs scale): 6; Color: Dark grey to black; Luster: Dull or earthy; Crystal structure: Aphanitic (fine-grained); Cleavage: None/Irregular; 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 specimen has been rounded and smoothed by water erosion in a river or coastal environment.

Uses & applications

Crushed basalt is used in construction for road base, concrete aggregate, and railroad ballast. Fine-grained pebbles are often used in landscaping and decorative aquariums.

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 common on the Moon and Mars.

Field identification & locations

Identify by its dark color, heavy weight (density), and fine-grained texture. It lacks visible large crystals. Commonly found in volcanic regions and riverbeds transporting volcanic material.

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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