igneous
Basalt with Vesicular Surface
Basalt (Mafic Extrusive)
Hardness: 6.0; Color: Dark gray to black, often weathering to tan/brown; Luster: Dull/earthy to sub-metallic; Structure: Fine-grained (aphanitic) with small pits or vesicles; Specific Gravity: 2.8–3.0.
- Hardness
- 6
- Color
- Dark gray to black, often weathering to tan/brown
- Luster
- Dull/earthy to sub-metallic
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Physical properties
Hardness: 6.0; Color: Dark gray to black, often weathering to tan/brown; Luster: Dull/earthy to sub-metallic; Structure: Fine-grained (aphanitic) with small pits or vesicles; 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. This specimen appears weathered and may contain secondary mineral infilling in its pores.
Uses & applications
Commonly used as aggregate in construction, road base, concrete, and railroad ballast. Highly weathered or high-quality specimens are occasionally used in landscape design.
Geological facts
Basalt is the most common rock type in Earth's crust and makes up most of the ocean floor. It is also found extensively on the Moon and Mars.
Field identification & locations
Identify in the field by its dark color, heavy weight (density), and fine-grained texture. It often shows 'vesicles' (gas bubble holes) or a rusty exterior from iron oxidation. Found worldwide in volcanic regions.
