metamorphic
Red Quartzite
Quartzite (primarily SiO2)
Hardness: 7 (Mohs scale), Color: Reddish-brown due to iron oxide inclusions, Luster: Vitreous to dull, Crystal Structure: Trigonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: Reddish-brown due to iron oxide inclusions, Luster: Vitreous to dull, Crystal Structure: Trigonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone. Specifically, heat and pressure cause the quartz grains to recrystallize and fuse together. Often associated with Proterozoic or Paleozoic geological formations.
Uses & applications
Used in construction as crushed stone or decorative facing, railway ballast, and in some cases as an abrasive. Polished varieties are used in landscaping and as ornamental stones.
Geological facts
Quartzite is so tough that it often survives intense erosion better than the rocks surrounding it, leading to the formation of ridges and resistant hills called monadnocks.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and its grainy, sandpaper-like texture that has been 'fused' into a glassy mass. Does not fizz with acid, unlike limestone or marble.
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