igneous
Vesicular Basalt
Basalt (Mafic Extrusive Volcanic Rock)
Hardness: 6-7 (Mohs scale), Color: Dark grey to black or brownish when weathered, Luster: Dull/Earthy, Crystal Structure: Aphanitic (fine-grained), Texture: Vesicular (contains gas bubble cavities), Specific Gravity: 2.8 - 3.0
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Physical properties
Hardness: 6-7 (Mohs scale), Color: Dark grey to black or brownish when weathered, Luster: Dull/Earthy, Crystal Structure: Aphanitic (fine-grained), Texture: Vesicular (contains gas bubble cavities), Specific Gravity: 2.8 - 3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. The specimen is likely from the Ethiopian Highlands, a region dominated by massive Tertiary flood basalts known as the Ethiopian Trap Series.
Uses & applications
Used primarily in construction as aggregate for roads, railroad ballast, and concrete. It is also used as a thermal insulator in its 'rock wool' form.
Geological facts
Basalt is the most common volcanic rock on Earth and covers much of the ocean floor. The provided coordinates (9.0°N, 38.7°E) place this find in Addis Ababa, which is situated directly on the volcanic Entoto and Addis Ababa Basalt formations.
Field identification & locations
Identify in the field by its dark color, heavy weight (relative to size), and characteristic holes or pits (vesicles). It is commonly found in Ethiopia's volcanic plateaus. Collectors look for specimens with secondary mineral infills like zeolites or opal.
