metamorphic
Banded Pebble (Metamorphic Slate or Gneiss with Quartz Veining)
Metamorphic Rock with Quartz/Calcite Veins
Hardness 3.0-7.0 depending on mineral composition, dark gray to black host rock with smooth rounded water-worn texture and prominent white quartz/calcite veins, dull to vitreous luster, fine-grained microcrystalline structure
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Physical properties
Hardness 3.0-7.0 depending on mineral composition, dark gray to black host rock with smooth rounded water-worn texture and prominent white quartz/calcite veins, dull to vitreous luster, fine-grained microcrystalline structure
Formation & geological history
Formed through regional metamorphism where fine-grained sedimentary mudstone or shale was subjected to heat and pressure, followed by hydrothermal fluid intrusion that filled fractures with white minerals like quartz or calcite. Subsequently smoothed by wave or river erosion into a beach/river pebble.
Uses & applications
Used primarily as decorative garden stone, landscaping accent, polished pocket stones, or for artisanal jewelry and crafts
Geological facts
The distinct white lines crosscutting the dark matrix are called hydrothermal veins. They form when mineral-rich hot fluids are injected into cracks within the rock under pressure and crystallize as they cool.
Field identification & locations
Identified in the field by its distinctive rounded beach-pebble shape with high-contrast white cross-cutting veins traversing a dark fine-grained host matrix. Commonly found along gravel beaches, riverbeds, and glacial till deposits worldwide.
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