metamorphic
Foliated schist, likely mica schist
Mica schist; chiefly quartz (SiO₂), muscovite/biotite mica, and feldspar
AI-generated identification · may be incorrectCoarse, strongly foliated and layered texture with silvery-gold reflective mica, gray quartz, and dark biotite. Mohs hardness is about 2–3 for mica and 6–7 for quartz; mica has perfect cleavage, while the rock splits along foliation. Specific gravity is typically 2.6–2.8.
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Physical properties
Coarse, strongly foliated and layered texture with silvery-gold reflective mica, gray quartz, and dark biotite. Mohs hardness is about 2–3 for mica and 6–7 for quartz; mica has perfect cleavage, while the rock splits along foliation. Specific gravity is typically 2.6–2.8.
Formation & geological history
Formed when shale or other clay-rich sediment was buried and subjected to elevated temperature and pressure, recrystallizing into aligned mica. It commonly represents Paleozoic metamorphism; rocks of this type are plausible near 40.0°N, 75.1°W in the Appalachian Piedmont.
Uses & applications
Used locally as decorative stone, landscape rock, fill, and occasionally building or roofing stone. Attractive mica-rich pieces are collected, but ordinary specimens have modest value.
Geological facts
The glitter comes from broad mica flakes reflecting light, not metallic metal. Its pronounced foliation records the direction of ancient tectonic compression.
Field identification & locations
Identify it by visible aligned mica flakes, glittery foliation, and easy splitting into thin sheets; unlike granite, it is distinctly layered rather than massive. Common in the Appalachian region, including southeastern Pennsylvania and nearby New Jersey.
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