igneous
Vesicular Basalt (or Porphyritic Scoria)
Vesicular Basalt
Hardness: 5-6 (Mohs scale); Color: Light grey to dark grey/reddish with dark phenocrysts; Luster: Dull/Earthy; Structure: Amorphous/Fine-grained with numerous gas holes (vesicles); Specific Gravity: 2.7-3.3
- Hardness
- 5-6 (Mohs scale)
- Color
- Light grey to dark grey/reddish with dark phenocrysts
- Luster
- Dull/Earthy
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Physical properties
Hardness: 5-6 (Mohs scale); Color: Light grey to dark grey/reddish with dark phenocrysts; Luster: Dull/Earthy; Structure: Amorphous/Fine-grained with numerous gas holes (vesicles); Specific Gravity: 2.7-3.3
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava. The holes (vesicles) are created by trapped gas bubbles that escaped as the lava solidified. They are found in volcanic regions of all ages, from recent eruptions to ancient tectonic sites.
Uses & applications
Used in landscaping, as a lightweight aggregate in concrete, for insulation, or as a decorative stone in aquariums. Can be used as an abrasive (pumice-like) depending on density.
Geological facts
Vesicular rocks like this are often light enough to float if they have a high enough gas-to-rock ratio (though basalt usually sinks). The dark spots in this specific specimen appear to be mineral 'phenocrysts' or secondary mineral infills (amygdules).
Field identification & locations
Identify in the field by its 'pock-marked' appearance and relatively heavy weight compared to pumice. Often found near shield volcanoes or Rift Valley formations.
