metamorphic
Garnet Schist
Garnetiferous Micaceous Schist
Hardness: 6.5-7.5 (garnet) 2-3 (mica matrix); Color: Reddish-brown crystals in a silvery-grey or black matrix; Luster: Vitreous to resinous (garnet) and pearly/metallic (mica); Crystal Structure: Isometric garnets in foliated sheets; Cleavage: None (garnet); Specific Gravity: 3.5-4.3
- Hardness
- 6
- Color
- Reddish-brown crystals in a silvery-grey or black matrix
- Luster
- Vitreous to resinous (garnet) and pearly/metallic (mica)
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Physical properties
Hardness: 6.5-7.5 (garnet) 2-3 (mica matrix); Color: Reddish-brown crystals in a silvery-grey or black matrix; Luster: Vitreous to resinous (garnet) and pearly/metallic (mica); Crystal Structure: Isometric garnets in foliated sheets; Cleavage: None (garnet); Specific Gravity: 3.5-4.3
Formation & geological history
Formed under regional metamorphism of pelitic sedimentary rocks (shale/mudstone) at intermediate to high temperatures and pressures. Often associated with mountain-building events in the Proterozoic or Paleozoic eras.
Uses & applications
Garnets are used as industrial abrasives (sandpaper, waterjet cutting) and as gemstones. The schist host rock is sometimes used as decorative stone or for geological study.
Geological facts
Garnets are index minerals used by geologists to determine the degree of metamorphism a rock has undergone. The deep red color of the garnet was once believed to provide protection against wounds and poison.
Field identification & locations
Identified in the field by the presence of hard, dodecahedral red crystals embedded in a flaky, foliated micaceous matrix. Common in metamorphic belts like the Appalachians, Alps, and Himalayas. Collectors should look for well-formed almandine garnet dodecahedrons protruding from the schist layers.
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