metamorphic

Garnet Schist

Almandine-Muscovite Schist

Hardness: 3.5 (matrix) to 7.5 (garnets); Color: Silvery-gray matrix with reddish-brown inclusions; Luster: Pearly to submetallic (mica) and vitreous (garnet); Crystal structure: Monoclinic (mica) and Isometric (garnet); Cleavage: Perfect basal cleavage in the mica matrix; Specific gravity: 2.8 - 4.3.

Hardness: 3
Color: Silvery-gray matrix with reddish-brown inclusions
Luster: Pearly to submetallic (mica) and vitreous (garnet)

Identified March 14, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed through regional metamorphism of clay-rich sedimentary rocks (pelites) such as shale. Under high pressure and moderate to high temperatures, minerals recrystallize to form oriented mica flakes and porphyroblasts of garnet. Typical geologic age ranges from Precambrian to Cenozoic depending on the mountain-building event.

Uses & applications

Used primarily as a decorative stone, geological study specimen, and source of industrial abrasives (garnet). Higher quality garnets within the rock may be extracted for semi-precious gemstones, though in schist, they are often fractured.

Geological facts

The 'sparkle' in this rock comes from oriented muscovite mica flakes. The garnets are 'index minerals,' meaning they tell geologists the specific level of pressure and temperature the rock reached during its formation deep underground.

Field identification & locations

Identify by looking for a 'foliated' or layered silvery appearance that glitters in the light, containing hard, rounded red-brown crystals. Common in mountain belts like the Appalachians, Alps, and Himalayas. Rock collectors look for well-formed dodecahedron garnet crystals protruding from the mica.