metamorphic

Biotite-rich schist (probable)

Mica schist; chiefly biotite mica, quartz, and feldspar

AI-generated identification · may be incorrect

Dark brown-black, platy and sparkly with a micaceous luster and visible foliation; individual mica flakes have Mohs hardness about 2.5–3, while quartz is 7. Crystals are typically fine to medium grained, with excellent mica cleavage and low-to-moderate density (~2.7–3.0).

Identified September 16, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when shale or mudstone underwent regional metamorphism, causing mica and other minerals to recrystallize and align under heat and pressure. Commonly Paleozoic or Precambrian, though age varies by locality.

Uses & applications

Used locally as decorative stone, landscaping aggregate, and occasionally dimension stone; attractive specimens are collected, but it is not usually a gemstone.

Geological facts

The glitter comes from reflective biotite cleavage surfaces, and the rock may split into thin sheets along its foliation. Its composition can grade toward gneiss if mineral grains become coarser and compositional banding develops.

Field identification & locations

Look for strong planar layering, abundant dark flexible mica flakes, and quartz/feldspar grains; a steel nail may scratch mica but not quartz. Common in regional metamorphic belts worldwide, including the Appalachians and New England.