igneous

Basalt (Water-worn pebble)

Basalt (Aphanitic mafic volcanic rock)

Hardness: 6.0 on Mohs scale; Color: Dark grey to black; Luster: Dull/Earthy (weathered); Crystal structure: Microcrystalline (aphanitic); Cleavage: None; Specific Gravity: 2.8 - 3.0

Hardness: 6
Color: Dark grey to black
Luster: Dull/Earthy (weathered)

Identified March 21, 2026More igneous →

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Physical properties

Hardness: 6.0 on Mohs scale; Color: Dark grey to black; Luster: Dull/Earthy (weathered); Crystal structure: Microcrystalline (aphanitic); Cleavage: None; 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 rounded and smoothed by water erosion in a river or beach environment.

Uses & applications

Basalt is used extensively in construction (as crushed stone for road base or concrete), for high-quality floor tiles, and as a material for 'hot stone' massage therapy due to its heat retention.

Geological facts

Basalt is the most common rock type in the Earth's crust, making up most of the ocean floor. It is also common on the Moon (the 'Maria' are basaltic plains) and Mars.

Field identification & locations

Identify in the field by its dark color, heavy weight compared to other similar-sized pebbles, and lack of visible crystals to the naked eye. Commonly found on volcanic islands and coastal areas near oceanic ridges.

Other igneous specimens

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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

Magnetite

Iron(II,III) oxide (Fe3O4)

mineral

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral

Blue Apatite

Apatite (Group), Ca5(PO4)3(F,Cl,OH)

mineral

Magnetite

Magnetite (Fe3O4)

mineral