metamorphic
Quartzite (River Cobble)
Quartzite (predominantly SiO2)
Hardness: 7 (Mohs scale); Color: White to grey interior with a tan/brown weathered rind; Luster: Vitreous to dull; Crystal structure: Non-foliated, granular; Cleavage: None (conchoidal to irregular fracture); Specific gravity: 2.6 - 2.7
- Hardness
- 7 (Mohs scale)
- Color
- White to grey interior with a tan/brown weathered rind
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: White to grey interior with a tan/brown weathered rind; Luster: Vitreous to dull; Crystal structure: Non-foliated, granular; Cleavage: None (conchoidal to irregular fracture); Specific gravity: 2.6 - 2.7
Formation & geological history
Formed from the metamorphism of quartzose sandstone through heat and pressure, typically in orogenic (mountain-building) belts. This specific specimen is a 'river cobble,' meaning its rounded exterior was shaped by fluvial erosion over thousands of years.
Uses & applications
Commonly used in construction as crushed stone for road ballast, as a decorative stone in landscaping, and historically for stone tools due to its hardness and predictability when fracturing.
Geological facts
Quartzite is so hard that it will scratch glass and steel. In many cases, the metamorphism is so complete that the rock will break through the individual quartz grains rather than around them, distinguishing it from sandstone.
Field identification & locations
Identify in the field by its extreme hardness and sugary, crystalline interior texture. Look for rounded 'potatoes' in riverbeds or glacial tills. It is extremely resistant to chemical weathering.
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