igneous
Weathered Basalt with Iron Staining
Aphanitic Mafic Volcanic Rock
Hardness: 5-6 Mohs. Color: Dark gray to black internally, with yellowish-brown to orange surface oxidation. Luster: Dull to earthy. Texture: Fine-grained (aphanitic). Structure: Massive/Vesicular.
- Hardness
- 5-6 Mohs
- Luster
- Dull to earthy
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Physical properties
Hardness: 5-6 Mohs. Color: Dark gray to black internally, with yellowish-brown to orange surface oxidation. Luster: Dull to earthy. Texture: Fine-grained (aphanitic). Structure: Massive/Vesicular.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or near the Earth's surface. The orange-brown coloration is due to the chemical weathering of iron-bearing minerals like olivine and pyroxene into limonite or goethite.
Uses & applications
Primarily used in construction as crushed stone for road base, concrete aggregate, and railroad ballast. Exceptionally weathered pieces have little industrial use but are geologically indicative of surface exposure.
Geological facts
Basalt is the most common rock type in the Earth's crust, making up most of the ocean floor. The yellowish hue on this piece is essentially geological rust.
Field identification & locations
Identify by its heavy weight (high specific gravity), dark interior, and fine-grained texture. Found globally in volcanic fields and oceanic crust. Look for dark rock with rusty outer rinds.
