igneous
Basalt with Weathering Rind
Basalt (Mafic Volcanic Rock)
Hardness: 6 (Mohs scale); Color: Dark grey to black interior with a light brown or tan weathered exterior (rind); Luster: Dull to sub-metallic; Structure: Fine-grained/aphanitic; Specific Gravity: 2.8-3.0.
- Hardness
- 6 (Mohs scale)
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6 (Mohs scale); Color: Dark grey to black interior with a light brown or tan weathered exterior (rind); Luster: Dull to sub-metallic; 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 or very near the surface of a terrestrial planet or the moon. The brownish exterior is caused by chemical weathering (oxidation) of iron-bearing minerals over time.
Uses & applications
Extensively used in construction as aggregate for concrete and asphalt, road base, railroad ballast, and as high-quality building stone or pavers.
Geological facts
Basalt is the most common rock type in the Earth's crust, making up most of the ocean floor. It is also the primary rock type on the Moon, Mars, and Venus.
Field identification & locations
Identify in the field by looking for a heavy, dark-colored, fine-grained rock. The presence of a distinct weathered 'crust' that hides a dark interior when chipped is a classic hallmark of basaltic exposure.
