igneous

Basalt (River Pebble)

Extrusive mafic igneous rock

Hardness: 6 (Mohs); Color: Dark grey to olive-brown; Luster: Dull/Earthy (aphanitic texture); Crystal structure: Fine-grained/Microcrystalline; Specific gravity: 2.8 - 3.0

Hardness: 6 (Mohs)
Color: Dark grey to olive-brown
Luster: Dull/Earthy (aphanitic texture)

Identified April 7, 2026More igneous →

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Physical properties

Hardness: 6 (Mohs); Color: Dark grey to olive-brown; Luster: Dull/Earthy (aphanitic texture); Crystal structure: Fine-grained/Microcrystalline; 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 and smoothed by water erosion in a fluvial (river) environment.

Uses & applications

Used in construction as aggregate, road base, and decorative landscaping. High quality specimens are used for 'hot stone' massage and aquarium decor.

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 and Mars.

Field identification & locations

Identify in the field by its dark color, heavy weight (density), and lack of visible crystals. Commonly found in volcanic regions or 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