metamorphic
Quartzite Cobble
Quartzite (SiO2)
Hardness: 7 (Mohs scale), Color: tan to light brown, Luster: dull to vitreous, Structure: granular crystalloblastic, Specific Gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: tan to light brown, Luster: dull to vitreous, Structure: granular crystalloblastic, Specific Gravity: 2.6-2.7
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone under intense heat and pressure, often found in glacial till or riverbeds.
Uses & applications
Construction aggregate, road ballast, landscaping, and historically used for stone tools due to its hardness and durability.
Geological facts
Quartzite is so tough that it often survives multiple cycles of erosion, usually appearing as rounded cobbles or pebbles in riverbanks long after softer rocks have dissolved.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by steel) and lack of reaction to acid. Common in glacial deposits and ancient stream beds globally.
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