igneous
Basalt with pale mineral veins/coating
Likely vesicular or altered basalt, with calcite or zeolite minerals
AI-generated identification · may be incorrectDark brown-black, fine-grained, dull to slightly vitreous basalt containing irregular white vein and crust material. Basalt is typically Mohs 5–6, with no visible cleavage and dense, generally specific gravity about 2.8–3.0; the white material may be softer calcite (Mohs 3) or harder zeolite (about 3.5–5.5).
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Physical properties
Dark brown-black, fine-grained, dull to slightly vitreous basalt containing irregular white vein and crust material. Basalt is typically Mohs 5–6, with no visible cleavage and dense, generally specific gravity about 2.8–3.0; the white material may be softer calcite (Mohs 3) or harder zeolite (about 3.5–5.5).
Formation & geological history
Basalt forms when low-silica lava cools rapidly at or near Earth’s surface, commonly in volcanic flows ranging from Precambrian to modern age. Later groundwater commonly deposits calcite, quartz, or zeolites in fractures and vesicles.
Uses & applications
Used widely as crushed aggregate, road stone, riprap, and dimension stone; attractive specimens are collected but are generally low-value.
Geological facts
The contrast between dark volcanic rock and white fracture fillings is characteristic of hydrothermal alteration. A vinegar test may fizz if the white material is calcite, though this should be done only on an inconspicuous spot.
Field identification & locations
Common in volcanic regions worldwide, including India’s Deccan Traps, Iceland, Hawaii, and the Pacific Northwest. A hand lens, streak test, hardness test, and acid test can help distinguish calcite from quartz or zeolite.
