igneous

Basalt

Basalt (Aphanitic Mafic Volcanic)

Hardness: 6.0 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal Structure: Microcrystalline/Aphanitic (fine-grained); Specific Gravity: 2.8 to 3.0

Hardness: 6
Color: Dark grey to black
Luster: Dull to sub-metallic

Identified March 26, 2026More igneous →

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Physical properties

Hardness: 6.0 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal Structure: Microcrystalline/Aphanitic (fine-grained); Specific Gravity: 2.8 to 3.0

Formation & geological history

Formed from the rapid cooling of low-viscosity lava rich in magnesium and iron at or very near the Earth's surface. This specimen appears water-worn or weathered, suggesting it was found in a riverbed or coastal area. Found in all geological ages from Archean to modern day.

Uses & applications

Used extensively in construction as road base, railroad ballast, and aggregate in concrete. High-quality specimens are used for 'hot stone' massage and increasingly in architectural stone veneers.

Geological facts

Basalt is the most common rock in the Earth's crust and makes up the majority of the ocean floor. It is also found on the Moon and Mars, forming the dark 'seas' or maria visible from Earth.

Field identification & locations

Identify in the field by its heavy weight (high density), dark color, and lack of visible crystals to the naked eye. It often shows conchoidal fracturing when chipped. Common in volcanic regions and along oceanic plate boundaries.

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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