igneous
Vesicular Basalt
Basalt (Mafic Extrusive Igneous Rock)
Hardness: 5-6 Mohs; Color: Dark grey to black, weathering to brown; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained) with vesicles; Cleavage: None; Specific Gravity: 2.8-3.0
- Hardness
- 5-6 Mohs
- Color
- Dark grey to black, weathering to brown
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 5-6 Mohs; Color: Dark grey to black, weathering to brown; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained) with vesicles; Cleavage: None; Specific Gravity: 2.8-3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava (basaltic) at the Earth's surface. The pits or 'vesicles' are formed by gas bubbles trapped in the cooling lava. Common in the Ethiopian Highlands volcanic province.
Uses & applications
Used extensively in construction as aggregate for roads, railroad ballast, and in concrete. Also used for stone tools traditionally or for decorative landscaping.
Geological facts
This specimen likely originates from the Cenozoic volcanic eruptions associated with the East African Rift system, which covers large areas of Ethiopia around Addis Ababa.
Field identification & locations
Identify in the field by its dark color, heavy weight (dense composition), and the presence of small holes (vesicles). It is the most common rock type in the Ethiopian Plateau.
