igneous

Basalt (Vesicular)

Extrusive mafic igneous rock; primarily (Ca, Na)(Mg, Fe, Al)(Si, Al)2O6 with (Ca, Na)(Al, Si)4O8

Hardness: 6 (Mohs scale); Color: Dark grey to black, weathering to brown; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Cleavage: None/conchoidal fracture; Specific gravity: 2.8 - 3.0. Note: This specimen appears vesicular/porous.

Hardness: 6 (Mohs scale)
Color: Dark grey to black, weathering to brown
Luster: Dull to sub-metallic

Identified March 15, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. Vesicular basalt specifically forms when gas bubbles are trapped in the cooling lava. It can range from Cenozoic to Precambrian in age.

Uses & applications

Used extensively in construction as road base, concrete aggregate, and railroad ballast. Larger pieces are used in landscaping and as 'lava rocks' for gas grills due to heat retention.

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, Mars, and Venus, indicating similar volcanic history on other planets.

Field identification & locations

Identify in the field by its dark color, heavy weight (high density), and fine-grained texture. It often shows 'holes' (vesicles) or a rusty exterior from iron oxidation. Common in volcanic regions like the Pacific Northwest, Hawaii, and Iceland.

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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