metamorphic
Garnet in Schist
Almandine Garnet in Mica-Schist (Fe3Al2(SiO4)3)
Hardness: 6.5-7.5 (garnet) vs 2-3 (mica matrix); Color: Deep burgundy/red garnet in gray-green matrix; Luster: Vitreous to sub-vitreous garnet; Crystal Structure: Isometric (dodecahedral crystals); Cleavage: None (garnet), perfect basal (schist matrix).
- Hardness
- 6
- Color
- Deep burgundy/red garnet in gray-green matrix
- Luster
- Vitreous to sub-vitreous garnet
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Physical properties
Hardness: 6.5-7.5 (garnet) vs 2-3 (mica matrix); Color: Deep burgundy/red garnet in gray-green matrix; Luster: Vitreous to sub-vitreous garnet; Crystal Structure: Isometric (dodecahedral crystals); Cleavage: None (garnet), perfect basal (schist matrix).
Formation & geological history
Formed through high-pressure, medium-to-high temperature regional metamorphism of clay-rich sedimentary rocks like shale. Typically found in mountain belts formed during the Paleozoic or Proterozoic eras.
Uses & applications
Garnets are used as industrial abrasives (sandpaper, waterjet cutting), gemstones in jewelry, and geological indicators for metamorphic grades.
Geological facts
Garnets are known as 'index minerals,' allowing geologists to determine the temperature and pressure conditions at which the rock formed. Almandine is the most common variety of the garnet group.
Field identification & locations
Identify by looking for hard, dark red, rounded or multi-faceted crystals embedded within a flaky, shimmering (micaceous) host rock. Common in the Appalachian Mountains, Alps, and Himalayas.
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