metamorphic
Garnet Schist
Almandine-Garnet Mica Schist
Hardness: 6.5-7.5 (garnets) and 2-3 (mica matrix); Color: Deep red to brown garnets in a silver-grey or bronze flaky matrix; Luster: Vitreous to resinous garnets, pearly/metallic matrix; Crystal Structure: Isometric (garnets), Monoclinic (mica); Cleavage: None in garnet, perfect basal in mica.
- Hardness
- 6
- Luster
- Vitreous to resinous garnets, pearly/metallic matrix
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Physical properties
Hardness: 6.5-7.5 (garnets) and 2-3 (mica matrix); Color: Deep red to brown garnets in a silver-grey or bronze flaky matrix; Luster: Vitreous to resinous garnets, pearly/metallic matrix; Crystal Structure: Isometric (garnets), Monoclinic (mica); Cleavage: None in garnet, perfect basal in mica.
Formation & geological history
Formed during regional metamorphism of clay-rich sedimentary rocks (pelites) under intermediate to high pressure and temperature. The garnets grow as porphyroblasts within the foliated mica layer. Formation typically occurs during orogenic (mountain-building) events.
Uses & applications
Garnets are used as industrial abrasives (sandpaper, waterjet cutting), and high-quality crystals are used in jewelry. The schist itself is sometimes used as decorative stone or for teaching geological principles.
Geological facts
The garnets inside schist are often dodecahedral crystals. This specific type of rock is a primary indicator of the 'garnet zone' in metamorphic facies, helping geologists map the pressure/heat history of a mountain range.
Field identification & locations
Identified by the presence of hard, rounded red-brown crystals protruding from a flaky, shiny, layered (foliated) rock. Common in the Appalachian Mountains, Alps, and Himalayas. Collectors should look for garnets that are well-formed and distinct from the matrix.
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