igneous

Basalt (Vesicular)

Basalt (Mafic Extrusive Igneous Rock)

Hardness: 6-7 Mohs scale; Color: Dark grey to black, weathering to reddish-brown; Luster: Dull/Sub-metallic; Crystal structure: Aphanitic (fine-grained); Cleavage: None; Specific gravity: 2.8-3.0; Contains vesicles (gas bubbles).

Hardness: 6-7 Mohs scale
Color: Dark grey to black, weathering to reddish-brown
Luster: Dull/Sub-metallic

Identified March 18, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava at the Earth's surface. Vesicular basalt specifically forms when gas bubbles are trapped in the cooling lava. Found in volcanic regions and oceanic crusts throughout geological history.

Uses & applications

Used extensively in construction as crushed stone for road base, concrete aggregate, and railroad ballast. Larger pieces are used as landscaping rocks or 'lava rocks' for grills and garden decoration.

Geological facts

Basalt is the most common rock type on Earth's crust and also covers large areas of the Moon, Mars, and Venus. The dark 'seas' on the Moon (Maria) are actually ancient basaltic lava plains.

Field identification & locations

Identify in the field by its high density, dark color, and characteristic small holes (vesicles). It is commonly found in basalt flows, near volcanic vents, or as glacial till in certain regions. Collectors look for pieces with interesting gas bubble patterns or secondary mineral fillings (amygdules).

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