metamorphic
Quartzite
Quartzite (primarily Silicon Dioxide, SiO2)
Hardness: 7 on Mohs scale (scratches glass). Color: White to grey, sometimes pink or tan from iron oxides. Luster: Vitreous to dull. Crystal structure: Hexagonal (microcrystalline). Cleavage: None (conchoidal fracture).
- Hardness
- 7 on Mohs scale (scratches glass)
- Color
- White to grey, sometimes pink or tan from iron oxides
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale (scratches glass). Color: White to grey, sometimes pink or tan from iron oxides. Luster: Vitreous to dull. Crystal structure: Hexagonal (microcrystalline). Cleavage: None (conchoidal fracture).
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone. High heat and pressure cause the sand grains to recrystallize and fuse together into a dense, hard rock. This specimen appears to have been further shaped by water erosion or intentional knapping.
Uses & applications
Used in construction as crushed stone or decorative facing, in the manufacturing of glass and ceramics, and historically by indigenous peoples to create tools/arrowheads.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks in a landscape, forming prominent ridges and peaks. It is one of the hardest common rocks found in the Earth's crust.
Field identification & locations
Identify in the field by its extreme hardness (it will not be scratched by a steel knife) and its grainy, sugary texture. Look for it in mountainous regions where tectonic activity has occurred.
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