igneous

Basalt

Mafic Igneous Rock (composed of plagioclase feldspar and pyroxene)

Hardness: 6 (Mohs scale); Color: Dark grey to black, weathering to rust-brown; Luster: Dull/earthy; Crystal Structure: Aphanitic (fine-grained); Specific Gravity: 2.8 - 3.0.

Hardness: 6 (Mohs scale)
Color: Dark grey to black, weathering to rust-brown
Luster: Dull/earthy

Identified March 12, 2026More igneous →

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Physical properties

Hardness: 6 (Mohs scale); Color: Dark grey to black, weathering to rust-brown; Luster: Dull/earthy; Crystal Structure: Aphanitic (fine-grained); Specific Gravity: 2.8 - 3.0.

Formation & geological history

Formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic) at the Earth's surface or on the ocean floor. Most basaltic formations date from various Cenozoic volcanic events to the present day.

Uses & applications

Extensively used in construction as an aggregate for road bases and concrete. In industry, it is melted to create stone wool insulation. Also used as floor tiles and for landscaping.

Geological facts

Basalt is the most common rock type in the Earth's crust, covering most of the ocean floor. The dark patches on the Moon (the Lunar Maria) are also composed of basaltic lava flows.

Field identification & locations

Identify in the field by its dark color, heavy weight (relative to size), and very fine grain where individual crystals are not visible to the naked eye. Often exhibits 'desert varnish' or a pitted texture if weathered. Commonly found in volcanic regions and along 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