metamorphic
Likely slate or fine-grained metamorphic stone with quartz vein
Slate–phyllite, composed mainly of quartz, mica, and chlorite; the white vein is likely quartz
AI-generated identification · may be incorrectDark gray, fine-grained, dull to slight silky luster, with a prominent white quartz vein. Hardness is approximately 2.5–4 for the matrix and 7 for quartz; cleavage or planar splitting may be present, and specific gravity is about 2.7–2.8.
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Physical properties
Dark gray, fine-grained, dull to slight silky luster, with a prominent white quartz vein. Hardness is approximately 2.5–4 for the matrix and 7 for quartz; cleavage or planar splitting may be present, and specific gravity is about 2.7–2.8.
Formation & geological history
Formed when clay-rich sedimentary rock was regionally metamorphosed at low grade, commonly during mountain building; the quartz vein formed later from mineral-rich fluids filling a fracture. Exact geological age cannot be determined from the photograph.
Uses & applications
Used for roofing, tiles, paving, landscaping, and decorative stone; quartz-veined pieces are mainly collectible or educational. Typical value is about $1–$10 per small specimen, or up to $20–$50 for attractive polished examples.
Geological facts
The contrasting white material appears harder and more resistant to weathering than the dark host rock. The pieces may also be fragments of schist or metabasalt, which cannot be distinguished confidently from this image alone.
Field identification & locations
Look for planar splitting, fine layering, and a streak that is usually pale gray; quartz veins should scratch glass while the matrix generally does not. Common sources include metamorphic belts worldwide, especially Wales, New England, the Appalachians, and the Alps.
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