metamorphic
Veined slate or phyllite pebble
Metamorphosed shale; commonly slate (fine-grained phyllosilicates, quartz, and carbonate veins)
AI-generated identification · may be incorrectDark gray-green, fine-grained, dull to subtly silky luster, with pale intersecting mineral veins; likely Mohs 3–5 and weak-to-moderate cleavage, though the rounded shape is water-worn. The veins may be calcite or quartz.
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Physical properties
Dark gray-green, fine-grained, dull to subtly silky luster, with pale intersecting mineral veins; likely Mohs 3–5 and weak-to-moderate cleavage, though the rounded shape is water-worn. The veins may be calcite or quartz.
Formation & geological history
Formed when shale or mudstone was compressed and mildly metamorphosed during mountain building; the light veins later filled fractures with calcite or quartz. Exact geological age cannot be determined from the photograph.
Uses & applications
Used as a decorative or lapidary pebble, with slate also used for roofing, paving, tiles, and writing surfaces; this small specimen has little industrial value.
Geological facts
The contrasting veins record fluid movement through fractures after or during metamorphism. A steel nail may scratch softer slate, while calcite veins can fizz weakly with dilute hydrochloric acid.
Field identification & locations
Common in metamorphic terrains and stream gravels worldwide, including the Appalachians, Wales, and parts of Scandinavia. Identify it by its fine dark matrix, planar fabric, and sharply contrasting pale veins; a close inspection is needed to distinguish slate from phyllite or veined basalt.
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