metamorphic
Quartzite Cobble
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, beige, or white with possible iron staining; Luster: Dull to vitreous; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6 - 2.7.
- Hardness
- 7 on Mohs scale
- Color
- Tan, beige, or white with possible iron staining
- Luster
- Dull to vitreous
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, beige, or white with possible iron staining; Luster: Dull to vitreous; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6 - 2.7.
Formation & geological history
Formed from the metamorphism of quartz sandstone. Intense heat and pressure cause the quartz grains to recrystallize and fuse together. This specific specimen has been further shaped by water erosion in a river or glacial environment.
Uses & applications
Commonly used in construction as crushed stone for road beds, railway ballast, and in some decorative landscaping applications. Harder specimens are used as abrasives.
Geological facts
Quartzite is so hard and durable that it often outlasts the surrounding rocks; when sandstone metamorphoses into quartzite, it transitions from a rock that breaks around grains to one that breaks through them.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel blade) and its grainy, sandpaper-like texture that doesn't rub off. Commonly found in riverbeds, glacial tills, and mountainous regions across the globe.
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