igneous
Vesicular Basalt (or Scoria)
Mafic extrusive igneous rock with vesicles
Hardness: 5-6 Mohs. Color: Deep reddish-brown to dark grey. Luster: Dull to earthy. Structure: Vesicular (contains many small cavities). Texture: Fine-grained aphanitic matrix. Specific gravity: 2.8-3.0.
- Hardness
- 5-6 Mohs
- Color
- Deep reddish-brown to dark grey
- Luster
- Dull to earthy
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Physical properties
Hardness: 5-6 Mohs. Color: Deep reddish-brown to dark grey. Luster: Dull to earthy. Structure: Vesicular (contains many small cavities). Texture: Fine-grained aphanitic matrix. Specific gravity: 2.8-3.0.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava (basaltic) extruded at the Earth's surface. The pits or 'vesicles' are caused by gas bubbles being trapped as the lava solidified. Primarily Cenozoic to Holocene age in many active volcanic regions.
Uses & applications
Used in landscaping, high-temperature insulation, drainage systems, decorative stone, and as an abrasive in 'stone-washed' denim. Often collected by students as examples of volcanic textures.
Geological facts
The holes in this rock are called vesicles. If the holes make up more than half the volume of the rock, it is often referred to as Scoria. Basalt is the most common rock type in the Earth's crust and makes up the ocean floors.
Field identification & locations
Identify in the field by its dark color, heavy weight (relative to size, unless very vesicular), and the presence of small spherical or oval pits. Commonly found in volcanic fields, near oceanic ridges, and hotspots like Hawaii or Iceland.
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