Vesicular Basalt (or Scoraceous Basalt)

Physical Properties

Hardness: 5-6 (Mohs scale); Color: Dark grey to black, weathered to brown/tan; Luster: Dull to earthy; Texture: Vesicular (contains many circular holes or pits); Composition: Plagioclase feldspar, pyroxene, and olivine.

Formation & Geological History

Formed from 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. These are common in volcanic fields from the Cenozoic to recent times.

Uses & Applications

Commonly used in landscaping as 'lava rock', in construction for heat insulation and lightweight concrete, or in some cases as filtration media.

Geological Facts

If the vesicles are large and the rock is very lightweight, it is called scoria. Some vesicular basalts can be hundreds of thousands to millions of years old, often found in volcanic hotspots or mid-ocean ridges.

Field Identification & Locations

Identify in the field by looking for a heavy, dark rock with numerous, non-connected spherical or almond-shaped cavities. It is commonly found in basaltic lava flows in regions like Hawaii, Iceland, or the Pacific Northwest.

Identified on: 5/15/2026

Mode: Standard