igneous
Vesicular Basalt
Extrusive Basaltic Scoria (CaAl2Si2O8 / (Mg,Fe)2SiO4)
Color: gray to dark brown; Hardness: 5-6 Mohs; Lustre: Dull/Earthy; Texture: Vesicular (pitted with gas bubbles); Structure: Aphanitic with visible voids.
- Hardness
- 5-6 Mohs
- Color
- gray to dark brown
Identified More igneous →
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Physical properties
Color: gray to dark brown; Hardness: 5-6 Mohs; Lustre: Dull/Earthy; Texture: Vesicular (pitted with gas bubbles); Structure: Aphanitic with visible voids.
Formation & geological history
Formed during volcanic eruptions when lava containing high concentrations of gas flows out onto the surface. The pressure drops, gases expand to form bubbles (vesicles), and the lava solidifies rapidly, trapping the holes in the rock.
Uses & applications
Used in construction for road aggregates, railroad ballast, and ground cover; also popular as 'lava rock' for landscaping and gas grills.
Geological facts
The holes in this rock are actually shadows of ancient volcanic gases. This specific specimen appears water-worn, indicating it was likely transported by a river or waves after its volcanic formation.
Field identification & locations
Identify by its lightweight feel relative to size and the presence of numerous small holes (vesicles). Commonly found in volcanic fields, ancient lava flows, and coastal areas near volcanic islands.
