metamorphic
Quartzite Cobble
Metamorphosed Quartz Sandstone (SiO2)
Hardness: 7 (Mohs scale); Color: Tan, orange, or yellowish due to iron oxide staining; Luster: Vitreous to dull; Crystal structure: Non-foliated, granular; Fracture: Conchoidal to irregular; Specific gravity: 2.6-2.7
- Hardness
- 7 (Mohs scale)
- Color
- Tan, orange, or yellowish due to iron oxide staining
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Tan, orange, or yellowish due to iron oxide staining; Luster: Vitreous to dull; Crystal structure: Non-foliated, granular; Fracture: Conchoidal to irregular; Specific gravity: 2.6-2.7
Formation & geological history
Quartzite forms when quartz-rich sandstone is subjected to high heat and pressure, typically during mountain-building events. This specific specimen has been further shaped into a rounded cobble by water erosion in a river or coastal environment.
Uses & applications
Commonly used as crushed stone in construction, road ballast, and as a decorative landscaping stone. High-purity quartzite is used in glass making and electronics.
Geological facts
Quartzite is so hard that when it breaks, it fractures through the quartz grains rather than along the boundaries between them, unlike sandstone. It often preserves the texture of the original sand grains despite its intense transformation.
Field identification & locations
Identify in the field by its hardness (cannot be scratched by a steel knife) and its grainy, crystalline appearance. It is commonly found in riverbeds, glacial tills, and ancient mountain ranges.
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