igneous
Vesicular Basalt (River Pebble)
Vesicular Basalt
Hardness: 5-6 (Mohs); Color: Gray to olive-green; Luster: Dull/Earthy; Crystal structure: Aphanitic (fine-grained); Cleavage: None; Features: Pitted surface with vesicles.
- Hardness
- 5-6 (Mohs)
- Color
- Gray to olive-green
- Luster
- Dull/Earthy
Identified More igneous →
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Physical properties
Hardness: 5-6 (Mohs); Color: Gray to olive-green; Luster: Dull/Earthy; Crystal structure: Aphanitic (fine-grained); Cleavage: None; Features: Pitted surface with vesicles.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at the earth's surface. The holes (vesicles) were created by gas bubbles trapped in the cooling magma. This specific specimen has been rounded by fluvial (river) or glacial erosion.
Uses & applications
Used primarily in construction as crushed aggregate, road base, and for landscaping. Porous varieties are sometimes used for filtration or as decorative aquarium stones.
Geological facts
Basalt is the most common rock in the Earth's crust and makes up most of the ocean floor. When the vesicles are filled with secondary minerals like quartz or calcite, the holes are called amygdules.
Field identification & locations
Identify in the field by its weight (dense for its size), dark gray or greenish-gray color, and characteristic small pits or 'Swiss cheese' texture. Commonly found in volcanic regions or transported to riverbeds via water flow.
