igneous
Basalt
Basalt (Mafic volcanic rock)
Hardness: 5-6 (Mohs); Color: Dark gray, black, or reddish-brown when weathered; Luster: Dull to submetallic; Structure: Fine-grained, aphanitic; Specific Gravity: 2.8–3.0.
- Hardness
- 5-6 (Mohs)
- Color
- Dark gray, black, or reddish-brown when weathered
- Luster
- Dull to submetallic
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Physical properties
Hardness: 5-6 (Mohs); Color: Dark gray, black, or reddish-brown when weathered; Luster: Dull to submetallic; Structure: Fine-grained, aphanitic; Specific Gravity: 2.8–3.0.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at the Earth's surface. Given the coordinates (Addis Ababa, Ethiopia area), this is likely part of the Ethiopian Trap Basalts, formed during massive volcanic eruptions in the Oligocene epoch about 30 million years ago.
Uses & applications
Used widely in construction as crushed stone for road base, concrete aggregate, and railroad ballast. It is also used as dimension stone for paving and flooring.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. The location provided sits on the Ethiopian Highland Plateau, which is globally famous for its thick sequences of flood basalts.
Field identification & locations
Identify by its dark color, heavy weight (density), and lack of visible large crystals to the naked eye. In Ethiopia, it is the primary bedrock and readily available in riverbeds and outcrops.
