igneous

Vesicular Basalt or Scoria

Basalt (extrusive volcanic rock)

Hardness: 5-6 (Mohs scale); Color: Dark gray, black, or reddish-brown; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained) with vesicles; Specific gravity: 2.8-3.0.

Hardness: 5-6 (Mohs scale)
Color: Dark gray, black, or reddish-brown
Luster: Dull to sub-metallic

Identified April 7, 2026More igneous →

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Physical properties

Hardness: 5-6 (Mohs scale); Color: Dark gray, black, or reddish-brown; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained) with vesicles; Specific gravity: 2.8-3.0.

Formation & geological history

Formed from the rapid cooling and solidification of basaltic lava at the Earth's surface. The pits or 'texture' seen are vesicles, created by trapped gas bubbles that escaped as the lava hardened during volcanic eruptions.

Uses & applications

Used as an aggregate in construction, for road base, in landscaping (lava rocks), and sometimes as a natural abrasive (pumice-like) in industrial cleaning.

Geological facts

Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. The distinctive 'scaly' or 'pitted' texture in this specimen suggests it was near the top of a lava flow where gas escaping was most intense.

Field identification & locations

Identify in the field by its dark color, heavy weight relative to its size, and the presence of small holes or pits. It is commonly found in volcanic regions such as Iceland, Hawaii, and the Pacific Northwest.

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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.

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