metamorphic
Schist (Garnet-Mica Schist)
Garnet-Mica Schist (X-Y)3Z2(SiO4)3
Hardness: 6.5–7.5 (garnets), 2–2.5 (mica). Color: Tan, brown, or silvery matrix with dark red to black inclusions. Luster: Pearly to sub-metallic. Crystal structure: Foliated/Schistose texture. Cleavage: Perfect basal cleavage in mica components.
- Hardness
- 6
- Luster
- Pearly to sub-metallic
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Physical properties
Hardness: 6.5–7.5 (garnets), 2–2.5 (mica). Color: Tan, brown, or silvery matrix with dark red to black inclusions. Luster: Pearly to sub-metallic. Crystal structure: Foliated/Schistose texture. Cleavage: Perfect basal cleavage in mica components.
Formation & geological history
Formed through the regional metamorphism of shale or mudstone under intermediate to high pressure and temperature. This process transforms clay minerals into micas and produces garnets through recrystallization.
Uses & applications
Used primarily for decorative stone, garden pathways, and walling. Garnets within schists are sometimes mined for abrasive purposes (sandblasting) or as gemstones if the crystals are large and clear.
Geological facts
Schist is characterized by its 'schistosity,' a texture where mica flakes align in thin parallel layers, allowing it to split easily. The presence of garnets indicates that the rock was subjected to deep crustal temperatures.
Field identification & locations
Identify in the field by looking for a shimmering, glittery surface (mica) containing hard, rounded, dark-red crystals (garnets). It is commonly found in mountain belts and Precambrian shields worldwide.
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