igneous

Vesicular Basalt

Extrusive Mafic Igneous Rock (composed of Plagioclase feldspar, Pyroxene, and Olivine)

Hardness: 5-6 (Mohs scale); Color: Dark grey, black, or dark brown; Luster: Dull to earthy; Structure: Vesicular (contains numerous small gas bubbles or holes); Specific Gravity: 2.8 - 3.0

Hardness: 5-6 (Mohs scale)
Color: Dark grey, black, or dark brown
Luster: Dull to earthy

Identified March 29, 2026More igneous →

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Physical properties

Hardness: 5-6 (Mohs scale); Color: Dark grey, black, or dark brown; Luster: Dull to earthy; Structure: Vesicular (contains numerous small gas bubbles or holes); Specific Gravity: 2.8 - 3.0

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava (mafic) at the Earth's surface. The holes (vesicles) are created by gas bubbles trapped in the lava as it solidifies. Can range from modern volcanic eruptions to billions of years old.

Uses & applications

Used in construction as road aggregate, railroad ballast, and concrete. Vesicular varieties are often used in landscaping, as BBQ grill stones, or for artisanal stone carving.

Geological facts

Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. Large-scale basalt flows can create unique hexagonal columns, such as those at the Giant's Causeway.

Field identification & locations

Identify in the field by its dark color, heavy weight (relative to size, unless very porous), and the presence of small circular pits (vesicles). Found globally in volcanic regions like Hawaii, Iceland, and the Pacific Northwest of the USA.

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Blue Apatite

Fluorapatite (Ca5(PO4)3F)

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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)

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Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

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Blue Apatite

Apatite (Group), Ca5(PO4)3(F,Cl,OH)

mineral

Magnetite

Magnetite (Fe3O4)

mineral