metamorphic
Garnet in Quartzite
Garnet-bearing Quartzite (SiO2 + X3Y2(SiO4)3)
Hardness: 6.5-7.5 (Mohs scale), Color: Creamy white to tan matrix with dark reddish-purple inclusions, Luster: Vitreous to dull, Crystal structure: Hexagonal (quartzite matrix) and Isometric (garnet), Cleavage: None/Conchoidal
- Hardness
- 6
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Physical properties
Hardness: 6.5-7.5 (Mohs scale), Color: Creamy white to tan matrix with dark reddish-purple inclusions, Luster: Vitreous to dull, Crystal structure: Hexagonal (quartzite matrix) and Isometric (garnet), Cleavage: None/Conchoidal
Formation & geological history
Formed through the regional metamorphism of sandstone rich in quartz and clay impurities. Under high pressure and temperature, quartz grains recrystallize and aluminum-rich minerals transform into garnet crystals.
Uses & applications
Abrasives (industrial), architectural stone, and collector specimens. Quality garnets can be used in jewelry.
Geological facts
Quartzite is one of the most durable rocks on Earth. The presence of garnet marks it as having undergone significant metamorphic change, often deep within the Earth's crust.
Field identification & locations
Identify by looking for small, dark, rounded or dodecahedral (12-sided) crystal inclusions within a hard, grainy, sugary-textured light-colored rock that cannot be scratched by a steel knife.
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