metamorphic

Micaceous schist

Mica schist, commonly muscovite–biotite–quartz schist

AI-generated identification · may be incorrect

Typically gray to black, with abundant reflective mica flakes, quartz-rich speckles, and pronounced foliation or schistosity. Hardness is about 2–3 for mica and 7 for quartz; luster is pearly to vitreous, and cleavage is excellent in mica.

Identified September 10, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when shale or another clay-rich sediment undergoes medium-grade regional metamorphism, commonly during mountain building. Its exact age cannot be determined from the image; schists range from Precambrian to modern orogenic belts.

Uses & applications

Used locally as decorative facing stone, landscape rock, and occasionally roofing or paving where foliation is stable; attractive specimens are collected, but it is rarely a jewelry material.

Geological facts

The glittering flakes are likely mica, whose basal cleavage allows it to split into thin sheets. Dark coloration may indicate biotite, graphite, or amphibole mixed with lighter quartz and feldspar.

Field identification & locations

Identify it by strong planar foliation, glittering platy grains, and easy splitting along mica-rich layers; granite lacks this aligned fabric. Common in metamorphic mountain belts worldwide, including the Appalachians, Alps, Himalaya, and New England.