igneous

Vesicular Basalt (Amygdaloidal)

Amygdaloidal Basalt (Mafic volcanic rock)

Hardness: 5-6 Mohs; Color: reddish-brown to dark gray; Luster: dull to earthy; Structure: vesicular (pitted) with small amygdules (mineral-filled cavities); Texture: fine-grained (aphanitic).

Hardness: 5-6 Mohs
Color: reddish-brown to dark gray
Luster: dull to earthy

Identified March 28, 2026More igneous →

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Physical properties

Hardness: 5-6 Mohs; Color: reddish-brown to dark gray; Luster: dull to earthy; Structure: vesicular (pitted) with small amygdules (mineral-filled cavities); Texture: fine-grained (aphanitic).

Formation & geological history

Formed from the rapid cooling of magnesium and iron-rich lava at the Earth's surface. The pits (vesicles) are created by trapped gas bubbles. This specific specimen’s reddish hue is caused by the oxidation of iron minerals (weathering).

Uses & applications

Used primarily in construction as road base, railroad ballast, and concrete aggregate. Sometimes used in landscaping or as scoria for decorative garden beds.

Geological facts

Basalt is the most common rock type in the Earth's crust, making up most of the ocean floor. The reddish variant is often associated with ancient lava flows that cooled in oxygen-rich environments.

Field identification & locations

Identify by its heavy weight (high specific gravity), small holes (vesicles), and a fine-grained feel. Common in volcanic regions such as the Pacific Northwest, Lake Superior region, and Hawaii.

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

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Blue Apatite

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

mineral

Magnetite

Magnetite (Fe3O4)

mineral