igneous
Vesicular basalt with secondary crystals
Basalt, likely zeolite- or calcite-lined vesicular basalt
AI-generated identification · may be incorrectDark gray-brown, fine-grained volcanic rock with abundant rounded vesicles; dull to slightly waxy luster and generally Mohs hardness 5–6. The cavity contains white, sparkling secondary crystals, possibly calcite or zeolite; crystal structure is mostly microscopic plagioclase and pyroxene.
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Physical properties
Dark gray-brown, fine-grained volcanic rock with abundant rounded vesicles; dull to slightly waxy luster and generally Mohs hardness 5–6. The cavity contains white, sparkling secondary crystals, possibly calcite or zeolite; crystal structure is mostly microscopic plagioclase and pyroxene.
Formation & geological history
Formed when basaltic lava cooled rapidly, trapping gas bubbles; later groundwater deposited crystals in the cavities. The specimen cannot be assigned a precise geological age from the image, but vesicular basalts range from Precambrian to recent volcanic settings.
Uses & applications
Used mainly as a decorative or educational specimen; basalt is widely used for aggregate, road stone, riprap, and occasionally dimension stone. Collector value is modest unless the cavity crystals are unusually attractive or analytically identified.
Geological facts
Commonly called amygdaloidal basalt when vesicles are filled or partly filled with minerals. The white crystals may be calcite, quartz, or zeolite-group minerals, which require hardness, acid, or laboratory testing for confirmation.
Field identification & locations
Identify by its dark volcanic matrix, abundant gas cavities, and lack of visible large primary crystals; common sources include Hawaii, Iceland, India’s Deccan Traps, Oregon, and other volcanic regions. Estimated value: $5–$25 for a small common specimen, potentially $30–$100 if the cavity minerals are well formed and locality-documented.
