igneous

Basalt Pebble

Extrusive Mafic Volcanic Rock

Hardness: 6-7 (Mohs scale); Color: Dark grey to black; Luster: Dull/Matte (when weathered); Structure: Fine-grained/Aphanitic; Specific Gravity: 2.8-3.0

Hardness: 6-7 (Mohs scale)
Color: Dark grey to black
Luster: Dull/Matte (when weathered)

Identified February 6, 2026More igneous →

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Physical properties

Hardness: 6-7 (Mohs scale); Color: Dark grey to black; Luster: Dull/Matte (when weathered); Structure: Fine-grained/Aphanitic; 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 has been rounded by fluvial or marine erosion.

Uses & applications

Commonly used as an aggregate in construction (roads, concrete), for railroad ballast, and polished for decorative landscaping or river-stone jewelry.

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 extensively on the Moon and Mars.

Field identification & locations

Identify in the field by its dark color, heavy weight (relative to size), and lack of visible crystals. Commonly found in volcanic regions, riverbeds, and along shorelines.

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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