igneous

Basalt (River Pebble)

Basalt

Hardness: 6-7 Mohs; Color: Dark grey to black; Luster: Dull/Matte; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8-3.0

Hardness: 6-7 Mohs
Color: Dark grey to black
Luster: Dull/Matte

Identified April 1, 2026More igneous →

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Physical properties

Hardness: 6-7 Mohs; Color: Dark grey to black; Luster: Dull/Matte; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8-3.0

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava exposed at or very near the surface of a terrestrial planet or a moon. This specific specimen has been smooth-rounded by water erosion in a river or coastal environment.

Uses & applications

Commonly used in construction (aggregate), high-end landscaping, massage therapy (hot stones), and as a base material for road beds.

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 heavy weight (high density), dark color, and lack of visible crystals. Commonly found in volcanic regions or as rounded pebbles in riverbeds and on beaches.

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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