metamorphic
Graphite-bearing schist (probable)
Graphite–quartz–mica schist; chiefly graphite (C), quartz (SiO₂), and mica
AI-generated identification · may be incorrectDark gray, strongly glittery, foliated and flaky, with a micaceous luster; quartz-rich patches are lighter. Typical hardness is about 2–3 for graphite and 2–7 for the mixed rock; cleavage follows schistosity, and graphite may leave a gray mark.
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Physical properties
Dark gray, strongly glittery, foliated and flaky, with a micaceous luster; quartz-rich patches are lighter. Typical hardness is about 2–3 for graphite and 2–7 for the mixed rock; cleavage follows schistosity, and graphite may leave a gray mark.
Formation & geological history
Formed when carbonaceous shale or other organic-rich sediment was regionally metamorphosed, commonly during mountain building. Exact age cannot be determined from the photograph; occurrences range from Precambrian to younger metamorphic terranes.
Uses & applications
Mostly a collector specimen; graphite-rich material may be used for lubricants, refractories, pencils, electrodes, and carbon products, while schist is occasionally used as decorative stone or aggregate.
Geological facts
The sparkle likely comes from aligned mica flakes, while the black component may be graphite rather than metallic ore. A streak test and electrical-conductivity test can help distinguish graphite-rich schist from sulfide-bearing rock.
Field identification & locations
Common in metamorphic belts worldwide, including the Appalachians, New England, Canada, Scandinavia, and India. Check for foliation, soft gray-black streak, greasy feel, and possible conductivity; an acid test is generally uninformative.
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