igneous
Vesicular basalt (scoria)
Vesicular basalt; a mafic volcanic rock composed chiefly of plagioclase, pyroxene, and sometimes olivine
AI-generated identification · may be incorrectGray, fine-grained groundmass with abundant rounded gas cavities (vesicles); generally dull to slightly glassy. Hardness about 5–6 on Mohs; specific gravity varies with vesicle abundance, commonly around 2.0–2.8.
Identified More igneous →
Explore Vesicular basalt (scoria) in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Gray, fine-grained groundmass with abundant rounded gas cavities (vesicles); generally dull to slightly glassy. Hardness about 5–6 on Mohs; specific gravity varies with vesicle abundance, commonly around 2.0–2.8.
Formation & geological history
Forms when gas-rich basaltic lava cools rapidly at or near the surface, trapping bubbles. Such rocks form during volcanic eruptions and may be of many ages; the specimen’s age cannot be determined from the image.
Uses & applications
Used as lightweight aggregate, landscaping stone, and sometimes abrasive or drainage material; attractive examples are collected as volcanic specimens.
Geological facts
The cavities are preserved gas bubbles, not fossils. Dense vesicular basalt is often called scoria; very vesicle-rich, lighter-colored volcanic rock is typically called pumice.
Field identification & locations
Look for a dark-gray to black volcanic matrix and many irregular pores; basalt is commonly found near lava flows and volcanic fields. The pictured specimen appears basaltic, though exact identification requires closer examination.
