metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale. Color: White to grey (sometimes pink or yellow). Luster: Vitreous to dull. Crystal structure: Trigonal/Hexagonal (granular). Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- White to grey (sometimes pink or yellow)
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale. Color: White to grey (sometimes pink or yellow). Luster: Vitreous to dull. Crystal structure: Trigonal/Hexagonal (granular). Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone. High heat and pressure cause quartz grains to recrystallize and fuse together. Typically found in orogenic belts where tectonic plates collide.
Uses & applications
Used in construction as crushed stone or road ballast, as a dimension stone for floor tiles and countertops, and in industrial glass making or as a source of silica.
Geological facts
Quartzite is so tough that it often outlasts the rocks surrounding it, forming prominent ridges or mountain peaks. It will scratch glass easily, unlike softer lookalikes like limestone.
Field identification & locations
Identify in the field by its hardness (cannot be scratched by a steel knife) and its grainy, sandpaper-like texture that doesn't rub off. Common in mountainous regions and riverbeds.
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