igneous
Vesicular Basalt
Extrusive Mafic Igneous Rock (Vesicular Basalt)
Hardness: 5-6 Mohs; Color: dark grey to brownish-black; Luster: dull to sub-metallic; Crystal structure: Aphanitic (fine-grained) with vesicles; Density: High specific gravity for the matrix.
- Hardness
- 5-6 Mohs
- Color
- dark grey to brownish-black
- Luster
- dull to sub-metallic
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Physical properties
Hardness: 5-6 Mohs; Color: dark grey to brownish-black; Luster: dull to sub-metallic; Crystal structure: Aphanitic (fine-grained) with vesicles; Density: High specific gravity for the matrix.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at the earth's surface. The 'holes' (vesicles) are created by gas bubbles that were trapped in the lava as it solidified.
Uses & applications
Used in landscaping (lava rock), construction aggregate, road base, and as an abrasive in industrial applications.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. Small vesicular specimens like this are often mistaken for meteorites by amateur collectors due to their weight and appearance.
Field identification & locations
Identify in the field by its dark color, heavy weight (relative to size, unless very porous), and the presence of small spherical or ovoid voids. Found in volcanic regions like Hawaii, Iceland, and the Pacific Northwest.
