metamorphic

Dark metamorphic cobble, likely slate or phyllite

Foliated metamorphic rock, probably carbonaceous slate/phyllite; exact identification requires testing

AI-generated identification · may be incorrect

Dark gray, fine-grained, dull to slightly silky luster, with pale mineral veins and weak planar foliation visible on the rounded surface. Typical hardness is about 2.5–4.5 Mohs; composition may include microscopic mica, quartz, chlorite, and carbonaceous material.

Identified September 20, 2026More metamorphic →

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At a glance

Common name: Dark metamorphic cobble, likely slate or phyllite
Scientific name: Foliated metamorphic rock, probably carbonaceous slate/phyllite; exact identification requires testing
Category: metamorphic
Identified: September 20, 2026
Method: Standard

AI Estimated Value

About $1–$10 as a common landscaping cobble; $10–$30 if unusually attractive, large, or demonstrably local/geologically significant.

Not an official valuation

AI estimate for general interest only — not an appraisal. Actual value depends on condition, provenance, and market demand. Verify with a professional before buying, selling, or insuring.

This identification was generated by AI and may contain errors. Verify important details before relying on them — and never use an AI result to judge whether a specimen is safe to handle. Read the full disclaimer

Physical properties

Formation & geological history

Formed when clay-rich sedimentary rock was regionally metamorphosed under low-grade pressure and temperature, commonly during mountain building. Its precise geological age and origin cannot be determined from the photograph.

Uses & applications

Used as crushed aggregate, landscaping stone, roofing or paving slate when sufficiently fissile, and occasionally as an architectural stone; this rounded specimen has modest collector value.

Geological facts

The pale lines are likely quartz or calcite veins, while the dark body suggests fine mica-rich or carbonaceous rock. Rounding indicates transport by water, glacial action, or prolonged weathering.

Field identification & locations

Common in metamorphic belts worldwide, including Wales, New England, the Appalachians, and parts of Scandinavia. Check for splitting along foliation, a streak, hardness, acid reaction, and a fresh surface; a field photo cannot distinguish slate confidently from phyllite or dark schist.