igneous

Basalt

Mafic Igneous Rock

Hardness: 6 (Mohs); Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8 - 3.0

Hardness: 6 (Mohs)
Color: Dark grey to black
Luster: Dull to sub-metallic

Identified May 12, 2026More igneous →

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Physical properties

Hardness: 6 (Mohs); Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8 - 3.0

Formation & geological history

Formed from the rapid cooling of low-viscosity basaltic lava at or very near the Earth's surface. This specimen appears to be a river-worn or beach pebble, shaped by water erosion over many years.

Uses & applications

Used extensively in construction as road base, railroad ballast, and concrete aggregate. Denser varieties are used for high-quality floor tiles and decorative landscaping.

Geological facts

Basalt is the most common rock type in 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 heavy weight relative to size, dark color, and lack of visible crystals. Commonly found in volcanic regions, along shorelines, and in riverbeds.

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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