Mica-rich schist

Typically gray, silvery, or brown with a glittery foliated texture; abundant platy mica produces visible sparkle and perfect basal cleavage. Mica hardness is about 2–3 Mohs, quartz about 7; overall density is commonly 2.6–2.8 g/cm³.

Formed when shale or other clay-rich sedimentary rock underwent regional metamorphism, causing mica and quartz to recrystallize and align into foliation. Such rocks range from Precambrian to younger mountain-belt ages; the specimen’s exact age cannot be determined visually.

Used locally as decorative stone, landscaping material, and occasionally aggregate, though its pronounced foliation limits structural use. Attractive pieces are collected as mineral or teaching specimens.

The bright flakes are likely muscovite, while darker bronze-black flakes may be biotite; quartz may form the granular pale matrix. Mica-rich schist splits readily along its foliation.

Identify it by its layered, sparkly surface and flakes that separate with a knife or fingernail; it is commonly found in metamorphic mountain regions worldwide, including New England, the Appalachians, the Alps, and India. Value is typically $5–$25 for a small common specimen, or $30–$100+ for unusually attractive or labeled pieces.