metamorphic
Quartzite Cobble
Metamorphic rock primarily composed of Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Tan to light brown (due to iron stains); Luster: Vitreous to dull; Crystal structure: Non-foliated, granular; Cleavage: None (fractures conchoidally); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Tan to light brown (due to iron stains)
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan to light brown (due to iron stains); Luster: Vitreous to dull; Crystal structure: Non-foliated, granular; Cleavage: None (fractures conchoidally); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure. This specimen shows significant rounding from alluvial processes (water transport in rivers or beaches).
Uses & applications
Primarily used as construction aggregate, railway ballast, and decorative landscaping stone. High-purity quartzite is used to produce silica sand for glass making.
Geological facts
Quartzite is so hard and tough that it often outlasts the surrounding rock in weathering processes, resulting in prominent ridges or rounded river stones like this one. It is harder than steel and will easily scratch glass.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a knife) and sugary/granular texture where fractured. Commonly found in riverbeds, glacial tills, and mountainous metamorphic belts.
