igneous
Vesicular Basalt (or Scoria)
Vesicular Basalt
Hardness: 5-6 (Mohs scale), Color: light grey to dark grey/black (this specimen appears weathered/bleached), Luster: dull/earthy, Crystal structure: Aphanitic (fine-grained), Cleavage: None, Specific gravity: 2.8-3.0 (though feels lighter due to vesicles/pore space).
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Physical properties
Hardness: 5-6 (Mohs scale), Color: light grey to dark grey/black (this specimen appears weathered/bleached), Luster: dull/earthy, Crystal structure: Aphanitic (fine-grained), Cleavage: None, Specific gravity: 2.8-3.0 (though feels lighter due to vesicles/pore space).
Formation & geological history
Formed from the rapid cooling of lava rich in gas. As the lava erupts, dissolved gases (like CO2 or water vapor) expand and form bubbles; if the rock solidifies before the gas can escape, these bubbles are preserved as vesicles.
Uses & applications
Used widely in construction (aggregate, concrete), landscaping (lava rocks), and sometimes as a natural abrasive (pumice/scoria). Small handheld specimens are common for educational purposes.
Geological facts
The holes in this rock are called vesicles. When these holes later fill with minerals like quartz or calcite, the textures are called amygdales, and the rock is known as amygdaloidal basalt.
Field identification & locations
Identify in the field by looking for a fine-grained texture combined with varying sizes of circular or elliptical pits. Commonly found in volcanic fields, ocean ridges, and basaltic plateaus like the Deccan Traps or Columbia River Basalt Group.
