igneous

Vesicular Basalt (Scoria)

Vesicular Basalt

Hardness: 5-6 (Mohs scale); Color: Black, dark gray, or reddish-brown; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained) with prominent vesicles (gas bubbles); Specific Gravity: 2.5-3.0.

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

Identified April 5, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the rapid cooling of basaltic lava containing dissolved gases. As the lava erupts at the surface, gases expand and escape, leaving behind a 'bubbly' texture known as vesicles. It is typically found in volcanic fields and near cinder cones.

Uses & applications

Used widely in landscaping (lava rocks), as an aggregate in lightweight concrete, for insulation, and in aquarium filters. Small, high-quality specimens are popular for educational geology collections.

Geological facts

Scoria is similar to pumice, but it is denser and sinks in water, whereas pumice floats. The holes (vesicles) are often filled with secondary minerals over millions of years to form amygdaloidal basalt.

Field identification & locations

Identify in the field by its sponge-like appearance and dark color. It is much heavier than pumice but lighter than solid basalt. Look for it near volcanic vents or historical lava flows.

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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