metamorphic

Biotite-rich schist (mica schist)

Mica schist, chiefly quartz + biotite mica; possibly feldspar and minor sulfides

AI-generated identification · may be incorrect

Medium- to coarse-grained, strongly foliated rock with glittering black-brown biotite and pale quartz/feldspar. Mohs hardness ~2.5–3 for biotite and ~6–7 for quartz; mica has perfect basal cleavage, while quartz is vitreous and cleavage-free.

Identified September 2, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when shale or other clay-rich sediment was subjected to regional metamorphism, typically during mountain building; its exact age cannot be determined from the photograph and may range from Precambrian to recent tectonic belts.

Uses & applications

Used locally as decorative stone, landscaping material, and mineral-collecting specimens; its pronounced foliation makes it unsuitable for most structural construction.

Geological facts

The reflective flakes are biotite, whose cleavage allows it to split into thin elastic sheets. Any brassy metallic grains may be pyrite, but this cannot be confirmed visually from the image.

Field identification & locations

Identify it by its planar layering, sparkly mica flakes, and tendency to break along foliation; common in metamorphic mountain regions worldwide, including the Appalachians, New England, and western North America.