Schist (specifically Mica Schist)

Physical Properties

Hardness: 3.5–4.0; Color: Silvery-gray to brownish-gold; Luster: Pearly to metallic (sub-metallic); Crystal structure: Monoclinic (in individual mica flakes); Cleavage: Perfect basal cleavage (easily peels into flakes); Specific Gravity: 2.7–3.0.

Formation & Geological History

Formed by regional metamorphism of clay-rich sedimentary rocks like shale or mudstone under intermediate to high temperatures and pressures. This creates the characteristic 'schistosity' or foliation through the alignment of flat mica minerals.

Uses & Applications

Used historically as a decorative stone in architecture and flagstone. In industry, it can be crushed for construction fill or used as a source for certain minerals like graphite or garnet if present in high concentrations.

Geological Facts

Because schist is so heavily foliated, it often breaks effortlessly into thin plates. It is a common source of garnets and often hosts 'staurolite' or 'kyanite' crystals which are popular with mineral collectors.

Field Identification & Locations

Identify in the field by its distinct glittering or shiny appearance (due to mica) and its tendency to flake or peel when scratched with a knife. It is common in mountain belts like the Appalachians, Alps, and Himalayas.

Identified on: 4/23/2026

Mode: Standard