metamorphic
Garnet Schist
Almandine-bearing Mica Schist
Hardness: 6.5-7.5 (garnets) 2.5 (mica). Color: Grey/silvery background with reddish-brown almandine garnets. Luster: Vitreous to pearly/silvery. Crystal structure: Porphyroblastic. Foliation: Strong schistosity.
- Hardness
- 6
- Color
- Grey/silvery background with reddish-brown almandine garnets
- Luster
- Vitreous to pearly/silvery
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Physical properties
Hardness: 6.5-7.5 (garnets) 2.5 (mica). Color: Grey/silvery background with reddish-brown almandine garnets. Luster: Vitreous to pearly/silvery. Crystal structure: Porphyroblastic. Foliation: Strong schistosity.
Formation & geological history
Forms through regional metamorphism of clay-rich sedimentary rocks like shale. The distinctive red crystals (garnets) grow under high pressure and temperature conditions deep within the crust.
Uses & applications
The garnets are used as industrial abrasives (sandpaper, waterjet cutting) and as gemstones. The schist itself is occasionally used as decorative garden stone or building veneer.
Geological facts
Garnets are known as 'indicator minerals' used by geologists to determine the temperature and pressure history of an area. The schist matrix often contains high amounts of muscovite, giving it a sparkling silver appearance.
Field identification & locations
Identify by the presence of small, hard, rounded reddish crystals embedded in a flaky, layered, or 'glittery' matrix. Common in mountain belts like the Appalachians, Alps, and Himalayas.
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