Igneous

Crushed Rock (Basalt)

Basalt (Aphanitic Mafic Igneous Rock)

Hardness: 6 on Mohs scale; Color: Dark grey to charcoal black; Luster: Dull to sub-metallic; Structure: Fine-grained (aphanitic) due to rapid cooling; Cleavage: None; Specific Gravity: 2.8 - 3.0

Hardness: 6 on Mohs scale
Color: Dark grey to charcoal black
Luster: Dull to sub-metallic

Identified March 18, 2026More igneous →

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Physical properties

Hardness: 6 on Mohs scale; Color: Dark grey to charcoal black; Luster: Dull to sub-metallic; Structure: Fine-grained (aphanitic) due to rapid cooling; Cleavage: None; Specific Gravity: 2.8 - 3.0

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava at or near the Earth's surface. These are volcanic in nature and can date from recent eruptions to billions of years old.

Uses & applications

Extensively used in construction as aggregate for concrete and asphalt, road base, and railroad ballast. Some varieties are used in architectural stone and landscaping.

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 by its dark color, heavy weight (density), and lack of visible large crystals to the naked eye. Commonly found in quarries and near volcanic regions. Not rare for collectors, but essential for geological studies.

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

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Blue Apatite

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

mineral

Magnetite

Magnetite (Fe3O4)

mineral