metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: Gray, tan, and reddish-brown; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Gray, tan, and reddish-brown
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, tan, and reddish-brown; 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 sandstone under high heat and pressure. It is found in mountain belts globally, often dating back to the Proterozoic or Paleozoic eras.
Uses & applications
Used in construction as crushed stone or decorative facing, in metallurgy as a source of silica, and occasionally in glassmaking or as a semi-precious stone for lapidary work.
Geological facts
Quartzite is so durable that it often remains as mountain caps long after softer surrounding rocks have eroded away. It is often harder than the steel blade of a knife.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by steel) and its granular, sugary texture on freshly broken surfaces. Regularly found in riverbeds as rounded cobbles like this specimen.
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