igneous
Basalt with Weathered Rind
Basalt (Extrusive Mafic Igneous Rock)
Hardness: 6.0; Color: Dark grey to black interior, brownish-rusty exterior rind; Luster: Dull to sub-metallic; Structure: Fine-grained (aphanitic) to vesicular; Cleavage: None/Conchoidal fracture.
- Hardness
- 6
- Color
- Dark grey to black interior, brownish-rusty exterior rind
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6.0; Color: Dark grey to black interior, brownish-rusty exterior rind; Luster: Dull to sub-metallic; Structure: Fine-grained (aphanitic) to vesicular; Cleavage: None/Conchoidal fracture.
Formation & geological history
Basalt forms from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. This specimen shows a weathered outer crust (rind) caused by oxidation of iron-bearing minerals over years of exposure to water and air.
Uses & applications
Basalt is used extensively in construction as crushed stone for road base, railroad ballast, and concrete aggregate. It is also used as a dimension stone for floor tiles and landscaping.
Geological facts
Basalt is the most common rock in the Earth's crust and makes up the entirety of the ocean floor. It is also extremely common on the Moon and Mars.
Field identification & locations
Identify in the field by its high density (heavy for its size), dark interior color, and fine-grained texture. It often shows a brown or reddish weathering rind in temperate climates. Found globally in volcanic provinces.
