igneous

Vesicular Basalt with Oxidation

Scoriaceous Olivine Basalt (Mafic volcanic rock)

Hardness: 5-6 (Mohs scale), Color: Dark gray to black (base) with reddish-orange iron oxide staining, Luster: Dull/Earthy, Crystal Structure: Aphanitic (fine-grained), Cleavage: None, Specific Gravity: 2.8-3.0.

Identified March 26, 2026More igneous →

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Physical properties

Formation & geological history

Formed through the rapid cooling of magnesium-rich and iron-rich lava at the Earth's surface. The 'pits' or vesicles are caused by gas bubbles trapped in the cooling magma. Typically Cenozoic or younger in age.

Uses & applications

Used primarily in construction (road base, concrete aggregate), landscaping (lava rock), and as an abrasive in industrial applications. Low-quality specimens are mostly used for decorative garden stones.

Geological facts

Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. The reddish color in this specimen indicates chemical weathering where iron minerals have 'rusted' upon exposure to oxygen and water.

Field identification & locations

Identify in the field by the high density (weight), visible gas bubbles (vesicles), and rough sandpaper-like texture. Common in volcanic regions such as the Pacific Northwest, Hawaii, and Iceland. Collectors look for pieces with interesting mineral infills (amygdules).

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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)

mineral

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral

Blue Apatite

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

mineral

Magnetite

Magnetite (Fe3O4)

mineral