metamorphic

Biotite-rich schist (likely graphite schist)

Mica schist; chiefly biotite, with quartz and feldspar, possibly graphite

AI-generated identification · may be incorrect

Dark gray to black, strongly foliated with shiny mica surfaces and wrinkled cleavage; Mohs hardness about 2.5–3 for biotite and 6–7 for quartz, with vitreous to pearly luster. The specimen appears platy and splits along schistosity; exact identification requires testing.

Identified September 16, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when shale or clay-rich sediment was subjected to regional metamorphism, producing aligned mica minerals; commonly Paleozoic to Precambrian in exposed metamorphic belts.

Uses & applications

Used locally as decorative stone, landscaping material, and occasionally dimension stone, though its pronounced foliation makes it prone to splitting; mainly collected as a teaching or display specimen.

Geological facts

The reflective dark flakes are characteristic of biotite; graphite, if present, can make the rock unusually black and leave a gray streak. It may also resemble hornblende-bearing gneiss or slate.

Field identification & locations

Common in metamorphic mountain belts such as New England, the Appalachians, the Alps, and parts of Scandinavia. Identify it by visible aligned mica flakes, foliation, and easy splitting; a graphite streak or magnetic response can refine identification.