igneous

Basalt with Vesicle/Vug

Basalt (Aphanitic Mafic Igneous Rock)

Hardness: 6 (Mohs scale); Color: Dark grey to charcoal black; Luster: Dull/Earthly; Structure: Vesicular (containing small holes) or Aphanitic (fine-grained); Specific Gravity: 2.8 - 3.0

Hardness: 6 (Mohs scale)
Color: Dark grey to charcoal black
Luster: Dull/Earthly

Identified March 29, 2026More igneous →

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Physical properties

Hardness: 6 (Mohs scale); Color: Dark grey to charcoal black; Luster: Dull/Earthly; Structure: Vesicular (containing small holes) or Aphanitic (fine-grained); 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 during volcanic eruptions. The holes (vesicles) are created by trapped gas bubbles escaping as the rock solidifies.

Uses & applications

Extensively used in construction, specifically as road base, concrete aggregate, and railroad ballast. Polished basalt is used for flagstone, floor tiles, and countertop surfaces.

Geological facts

Basalt is the most common rock on the Earth's surface; most of the ocean floor is composed of it. It is also found on the Moon and Mars, forming the dark 'Maria' seen from Earth.

Field identification & locations

Identify by its heavy weight (density), dark color, and fine grain where crystals cannot be seen by the naked eye. Often found in volcanic fields or as river rocks in volcanic regions.

Other igneous specimens

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Blue Apatite

Fluorapatite (Ca5(PO4)3F)

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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