Vesicular Basalt (Aqueous Tumbled)

Physical Properties

Hardness: 6 (Mohs); Color: Dark brown, black, with iron oxidation (orange highlights); Luster: Dull to slightly vitreous when wet; Structure: Vesicular (pitted with gas bubbles); Cleavage: None/Conchoidal.

Formation & Geological History

Formed from the rapid cooling of low-viscosity, gas-rich basaltic lava at or near the Earth's surface. Extrusive igneous origin, typical of volcanic regions like Hawaii or Iceland.

Uses & Applications

Used as aggregate in construction, landscaping stones, barbecue rocks, and sometimes as an abrasive (lava rock pumice). Low-grade collectors value it for teaching petrology.

Geological Facts

The holes (vesicles) are created by gas bubbles that were trapped as the lava solidified. This specific specimen appears water-worn, suggesting it was recovered from a river or beach.

Field Identification & Locations

Identify in the field by its dark color, high density (relative to pumice), and distinctive 'Swiss cheese' porous surface. Commonly found in volcanic rift zones and coastal areas.

Identified on: 4/30/2026

Mode: Standard