igneous
Likely basalt with a pale mineral-filled vesicle
Vesicular basalt, probably containing calcite or zeolite (uncertain from image)
AI-generated identification · may be incorrectDark gray, fine-grained, dull to slightly glassy rock with an irregular cavity and pale crystalline filling; typical basalt hardness is about 6 Mohs, with no obvious cleavage and specific gravity around 2.8–3.0.
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Physical properties
Dark gray, fine-grained, dull to slightly glassy rock with an irregular cavity and pale crystalline filling; typical basalt hardness is about 6 Mohs, with no obvious cleavage and specific gravity around 2.8–3.0.
Formation & geological history
Formed when basaltic lava cooled rapidly at or near Earth’s surface, trapping gas bubbles; the cavity was later lined or filled by low-temperature groundwater minerals. Basalt commonly ranges from Precambrian to recent age.
Uses & applications
Used widely as crushed aggregate, road stone, riprap, and building stone; attractive mineral-filled pieces are mainly collected as specimens. Estimated value is roughly $2–$20, or $20–$75 if the cavity contains well-formed crystals.
Geological facts
The pale material may be calcite, quartz, or a zeolite such as stilbite; identification requires hardness, acid, streak, or laboratory testing.
Field identification & locations
Look for a dark, dense volcanic groundmass, vesicles, and tiny crystals; basalt is common in volcanic regions worldwide, including Hawaii, Iceland, India, and the Columbia River area. A steel scratch test and a drop of dilute hydrochloric acid can help distinguish quartz/zeolite from calcite.
