metamorphic
Quartzite (River Cobble)
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, beige, or white with iron staining; 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
- Tan, beige, or white with iron staining
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, beige, or white with iron staining; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal (granular); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone subjected to high heat and pressure. This specific specimen has been rounded and smoothed by water transport in a river or glacial environment.
Uses & applications
Used primarily in construction as crushed stone or ballast. Often used in landscaping and as decorative garden pebbles.
Geological facts
Quartzite is so tough that it often survives through multiple cycles of erosion that destroy softer rocks. It is harder than steel, meaning it will easily scratch a knife blade.
Field identification & locations
Identify in the field by its hardness (scratches glass) and its sugary, granular texture on fresh surfaces. Often found in riverbeds, glacial tills, or coastal beaches.
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