igneous
Likely vesicular basalt (pumice-like volcanic stone)
Vesicular basalt; predominantly plagioclase, pyroxene, and possibly olivine
AI-generated identification · may be incorrectGray, rounded, fine-grained and porous, with a dull to slightly earthy luster; hardness about 5–6 Mohs, no obvious cleavage, and moderate-to-high density unless highly vesicular. The surface texture suggests gas-bubble cavities, though the image cannot confirm mineral details.
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Physical properties
Gray, rounded, fine-grained and porous, with a dull to slightly earthy luster; hardness about 5–6 Mohs, no obvious cleavage, and moderate-to-high density unless highly vesicular. The surface texture suggests gas-bubble cavities, though the image cannot confirm mineral details.
Formation & geological history
Formed when mafic lava cooled rapidly while escaping gases created vesicles; likely Cenozoic or younger, but age cannot be determined visually. Common in volcanic fields, lava flows, beaches, and stream gravels.
Uses & applications
Used as aggregate, landscaping stone, abrasive, lightweight concrete component, and occasionally as a sculptural or teaching specimen; generally not jewelry quality.
Geological facts
Vesicular basalt is darker and denser than pumice, while pumice is usually much lighter and may float. Weathering can produce the pale gray-brown appearance shown here.
Field identification & locations
Look for a fine-grained dark-gray matrix, irregular pores, heavy feel, and weak attraction or no attraction to a magnet; a streak, acid test, and density test would improve identification. Common worldwide in volcanic regions and transported gravels.
