Vesicular Basalt (or Scoria)

Physical Properties

Hardness: 5-6 (Mohs); Color: Dark grey, charcoal, or reddish-brown; Luster: Dull/Earthy; Structure: Fine-grained/Aphanitic with vesiculed (holey) texture; Specific Gravity: 2.8–3.0

Formation & Geological History

Formed through the rapid cooling of magnesium-rich and iron-rich lava. The holes (vesicles) are created by gas bubbles that were trapped in the lava as it solidified near the Earth's surface.

Uses & Applications

Commonly used in landscaping as 'lava rock', in construction for lightweight concrete, as an abrasive in stone-washing jeans, and for thermal insulation.

Geological Facts

The holes in the rock are essentially snapshots of volcanic gases (like water vapor and CO2) that were escaping during an eruption millions of years ago. It is essentially frozen foam.

Field Identification & Locations

Identify by its 'Swiss cheese' appearance and lightweight feel compared to solid rocks. Found in volcanic regions like Hawaii, Iceland, and the Pacific Northwest, USA.

Identified on: 5/15/2026

Mode: Standard