metamorphic

Biotite schist (probable)

Mica schist, chiefly quartz + feldspar + biotite mica

AI-generated identification · may be incorrect

Dark gray-brown, strongly foliated and flaky, with sparkly mica-rich layers and lighter quartz/feldspar bands. Typical hardness is about 2.5–3 for biotite and 6–7 for quartz; cleavage is excellent in mica, with a generally low-to-moderate luster.

Identified September 16, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when shale or other clay-rich sediment was subjected to elevated temperature and pressure during regional metamorphism, commonly during mountain building. Its exact geological age cannot be determined from the photograph.

Uses & applications

Used locally as decorative stone, landscaping material, and occasionally dimension stone, though mica schist is weaker and less durable than granite. Attractive specimens may be collected for their foliation and sparkle.

Geological facts

The visible planar layering is schistosity, produced by aligned platy mica crystals. The specimen may also contain garnet or amphibole, but these cannot be confirmed from the image.

Field identification & locations

Likely identification requires confirming that flakes peel along foliation and that mica sparkles or separates into thin sheets; a streak, hardness, and close-up inspection would help. Common in metamorphic mountain belts worldwide, including the Appalachians, New England, Scotland, and the Alps.