igneous
Vesicular Basalt
Extrusive mafic igneous rock (Basalt with vesicular texture)
Hardness: 6-7 on the Mohs scale. Color: Dark grey, greenish grey, to black, often with a weathered surface. Luster: Dull, earthy. Texture: Vesicular to fine-grained (aphanitic), filled with small gas bubble cavities (vesicles). Specific Gravity: 2.8 - 3.0.
- Hardness
- 6-7 on the Mohs scale
- Luster
- Dull, earthy
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Physical properties
Hardness: 6-7 on the Mohs scale. Color: Dark grey, greenish grey, to black, often with a weathered surface. Luster: Dull, earthy. Texture: Vesicular to fine-grained (aphanitic), filled with small gas bubble cavities (vesicles). Specific Gravity: 2.8 - 3.0.
Formation & geological history
Formed from rapid cooling of mafic lava rich in dissolved gases. As the lava cools and solidifies on or near the Earth's surface, escaping gas bubbles leave tiny pits or cavities (vesicles) trapped within the rock matrix.
Uses & applications
Commonly used as construction aggregate, crushed stone for road bases, concrete aggregate, and decorative landscaping stone.
Geological facts
Basalt is the most common rock type in the Earth's crust, making up almost all of the ocean floors. When vesicles in basalt are later filled by secondary minerals like quartz, agate, or zeolites, the rock becomes amygdaloidal basalt.
Field identification & locations
Identified in the field by its dark color, fine grain, relative weight, and distinct tiny holes or pitted surface left by ancient gas bubbles. Commonly found along volcanic fields, riverbeds, and ocean beaches near volcanic terrain. Value: $1 - $5 for common field specimens.
