metamorphic

Biotite-bearing metamorphic rock, likely gneiss or schist

Mica-rich quartz–feldspar gneiss/schist; exact identification requires testing

AI-generated identification · may be incorrect

Gray to dark brown, coarse-grained, strongly foliated, with reflective black-brown biotite mica and lighter quartz/feldspar. Hardness is approximately 2.5–3 for mica and 6–7 for quartz/feldspar; nonmetallic to pearly luster, with mica cleavage and no obvious uniform crystal form.

Identified September 3, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when shale or granite was subjected to substantial heat and pressure during mountain-building, typically hundreds of millions to billions of years ago. The apparent cavity may be weathering, a former mineral pocket, or a fracture.

Uses & applications

Used locally as building stone, aggregate, landscaping rock, and decorative slabs; attractive specimens are collected but are generally not jewelry-grade.

Geological facts

Foliation reflects alignment of mica minerals and can cause the rock to split into layers. The silvery flashes are characteristic of mica rather than metal.

Field identification & locations

Look for planar banding or flaky cleavage, abundant mica, and resistance to scratching by a steel knife in quartz-rich areas; a glass-scratch test and close inspection of layering would help distinguish gneiss from schist. Common in Precambrian shields and mountain belts worldwide.