igneous

Basalt (Vesicular)

Basalt (Extrusive Mafic Igneous Rock)

Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull/Submetallic; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8-3.0; Contains small cavities (vesicles).

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

Identified March 29, 2026More igneous →

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Physical properties

Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull/Submetallic; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8-3.0; Contains small cavities (vesicles).

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava exposed at or very near a planetary surface. Vesicles indicate gas bubbles trapped during cooling. Usually from the Cenozoic era or younger when found in surface deposits.

Uses & applications

Used primarily in construction for road base, concrete aggregate, and railroad ballast. Small water-worn or weathered pieces like this are common in landscaping or as aquarium decor.

Geological facts

Basalt is the most common rock in Earth's crust and makes up most of the ocean floor. It is also found abundantly on the Moon and Mars.

Field identification & locations

Identify by its dark color, heavy weight for its size, and the presence of small pits (vesicles). Found globally in volcanic regions or riverbeds downstream from volcanic areas. Common in the Pacific Northwest and Hawaii.

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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)

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Magnetite

Magnetite (Fe3O4)

mineral