igneous

Vesicular Basalt

Extrusive mafic igneous rock; primarily (Ca,Na)(Mg,Fe,Al,Si)2O6 (Pyroxene) and (Ca,Na)Al(Al,Si)Si2O8 (Plagioclase Feldspar)

Hardness: 6 (Mohs scale); Color: Dark gray to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained) with visible vesicles (gas bubbles); Specific gravity: 2.8–3.0

Hardness: 6 (Mohs scale)
Color: Dark gray to black
Luster: Dull to sub-metallic

Identified March 14, 2026More igneous →

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Physical properties

Hardness: 6 (Mohs scale); Color: Dark gray to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained) with visible vesicles (gas bubbles); Specific gravity: 2.8–3.0

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava at the Earth's surface. The pitted texture (vesicles) occurs as gas bubbles are trapped in the cooling lava. Most found on Earth is from the Cenozoic era or younger due to plate tectonics.

Uses & applications

Used extensively as aggregate in construction, road base, concrete, and railroad ballast. Highly vesicular specimens (like scoria) are used in landscaping and as abrasive 'pumice stones' in cosmetics.

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 in abundance on the Moon and Mars.

Field identification & locations

Identify in the field by its dark color, heavy weight for its size, and the circular or almond-shaped pits on the surface. Commonly found in volcanic fields, oceanic islands (like Hawaii), and mid-ocean ridges.

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

mineral

Blue Apatite

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

mineral

Magnetite

Magnetite (Fe3O4)

mineral