igneous

Basalt with Scoria/Vesicular Texture

Extrusive Mafic Igneous Rock (primarily Plagioclase Feldspar and Pyroxene)

Hardness: 5-6 (Mohs scale); Color: Dark grey to black, weathering to brown; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained) with vesicular (porous) voids; Specific gravity: 2.8–3.0.

Hardness: 5-6 (Mohs scale)
Color: Dark grey to black, weathering to brown
Luster: Dull to sub-metallic

Identified March 26, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava exposed at or very near the surface. The holes (vesicles) are created by gas bubbles escaping as the lava solidifies. It can range in age from modern volcanic flows to billions of years old.

Uses & applications

Used extensively in construction as road base, railroad ballast, and aggregate in concrete. Highly vesicular varieties (scoria) are used in landscaping, as gas grill 'lava stones', and as lightweight abrasive materials.

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 (relative to size), and the presence of small holes or pits. It is commonly found in volcanic regions such as the Pacific Northwest (USA), Iceland, and Hawaii. For collectors, look for specimens with unique mineralization inside the vesicles (amygdules).

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