igneous
Vesicular Basalt
Basalt (SiO2 range 45-52%) with vesicular texture
Hardness: 5-6 (Mohs); Color: Dark gray to brownish-gray; Luster: Dull/Earthy; Structure: Aphanitic (fine-grained) with conspicuous vesicles (voids); Specific Gravity: 2.8-3.0
- Hardness
- 5-6 (Mohs)
- Color
- Dark gray to brownish-gray
- Luster
- Dull/Earthy
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Physical properties
Hardness: 5-6 (Mohs); Color: Dark gray to brownish-gray; Luster: Dull/Earthy; Structure: Aphanitic (fine-grained) with conspicuous vesicles (voids); Specific Gravity: 2.8-3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava. The holes (vesicles) are formed by gas bubbles escaping as the lava solidified. This specimen is likely from the Ethiopian Cenozoic volcanic province (Ethiopian Highlands), formed by plume-related volcanism.
Uses & applications
Used as aggregate in construction, road base, and landscaping. Due to its porous nature, it is sometimes used for water filtration or heat insulation.
Geological facts
The Addis Ababa region is situated on thick volcanic sequences. Vesicular basalt is common in rift zones like the East African Rift. These rocks provide the fertile soil found in much of the Ethiopian plateau after they weather down.
Field identification & locations
Identify by the presence of numerous small holes or cavities in a dense, dark stony mass. It is very common in the volcanic regions of Ethiopia. Collectors value it for showing clear volcanic activity indicators.
