igneous
Quartz-veined basaltic volcanic rock
Likely amygdaloidal basalt or andesite with quartz and feldspar vein material
AI-generated identification · may be incorrectDark brown, fine-grained, massive rock with a dull to weakly vitreous surface; white crystals/patches are probably quartz and/or calcite, with possible feldspar. Estimated hardness 5–7 overall; white material may be softer if calcite, and specific gravity is roughly 2.7–3.0.
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Physical properties
Dark brown, fine-grained, massive rock with a dull to weakly vitreous surface; white crystals/patches are probably quartz and/or calcite, with possible feldspar. Estimated hardness 5–7 overall; white material may be softer if calcite, and specific gravity is roughly 2.7–3.0.
Formation & geological history
Formed when mafic to intermediate lava cooled rapidly, later fractured and was infiltrated by silica- or carbonate-rich hydrothermal fluids. Age cannot be determined from the photograph; such rocks occur from Precambrian to recent volcanic terrains.
Uses & applications
Primarily a collector specimen; unaltered basalt and andesite are used as aggregate, riprap, roadstone, and occasionally building stone, while quartz-bearing material may be ornamental.
Geological facts
The brown coloration likely reflects oxidation of iron-bearing minerals. White vein fillings can be distinguished by testing: quartz resists scratching and does not fizz in dilute acid, whereas calcite fizzes and is softer.
Field identification & locations
Look for a fine-grained volcanic groundmass, scattered vesicles or fractures, and contrasting white veins. Common settings include volcanic arcs, lava flows, and hydrothermal zones; exact locality requires provenance or laboratory testing.
