igneous
Vesicular basalt (likely weathered/amygdaloidal basalt)
Basalt; predominantly plagioclase and pyroxene, with possible olivine and secondary zeolite/calcite infillings
AI-generated identification · may be incorrectDark gray-brown, fine-grained volcanic rock with numerous rounded vesicles and weathered reddish-brown surfaces; the cavity may be partly lined or filled by secondary minerals. Hardness is typically about 5–6 Mohs, dull to slightly earthy luster, massive texture, and no prominent cleavage.
Identified More igneous →
Explore Vesicular basalt (likely weathered/amygdaloidal basalt) in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Dark gray-brown, fine-grained volcanic rock with numerous rounded vesicles and weathered reddish-brown surfaces; the cavity may be partly lined or filled by secondary minerals. Hardness is typically about 5–6 Mohs, dull to slightly earthy luster, massive texture, and no prominent cleavage.
Formation & geological history
Formed when mafic lava cooled rapidly at or near Earth’s surface, trapping gas bubbles; later groundwater alteration can produce pale mineral coatings or amygdules. Basalt ranges from Precambrian to modern age, so an exact age requires locality data.
Uses & applications
Used as crushed aggregate, road stone, riprap, and building stone; attractive amygdaloidal pieces are collected, though this specimen appears mainly of modest educational value.
Geological facts
Vesicles distinguish it from most massive basalt; mineral-filled vesicles are called amygdules. Weathering commonly converts iron-bearing minerals to orange-brown oxides.
Field identification & locations
Look for a heavy, fine-grained dark matrix, abundant irregular or rounded holes, and weak attraction to a magnet if magnetite is present. Common worldwide in lava flows, volcanic islands, and oceanic crust; avoid calling it scoria unless it is very light and highly vesicular.
