Igneous

Basalt

Mafic Volcanic Rock (Primarily Plagioclase feldspar and Pyroxene)

Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull/Earthy; Crystal Structure: Aphanitic (fine-grained); Specific Gravity: 2.8–3.0. Shows vesicular texture (small pits).

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

Identified March 13, 2026More igneous →

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Physical properties

Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull/Earthy; Crystal Structure: Aphanitic (fine-grained); Specific Gravity: 2.8–3.0. Shows vesicular texture (small pits).

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. Common in oceanic crust and volcanic hotspots. Geological age varies globally from Archean to recent eruptions.

Uses & applications

Used extensively in construction as road base, railroad ballast, and concrete aggregate. High-quality specimens are used for 'lava rock' in grilling and landscaping, or as polished river stones for massage therapy.

Geological facts

Basalt is the most common rock type in the Earth's crust and even covers large parts of other planetary bodies like the Moon (lunar maria), Mars, and Venus.

Field identification & locations

Identify in the field by its dark color, heavy weight (density), and fine-grained texture. It often shows small holes where gas bubbles were trapped during cooling. Found globally in volcanic regions like Iceland, Hawaii, and the Columbia River Plateau.

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