metamorphic
Quartzite Cobble
Quartzite (principally SiO2)
Hardness: 7 Mohs; Color: Tan to off-white with minor iron staining; Luster: Dull/Waxy (weathered) to Vitreous (internal); Structure: Granular/Crystalline; Non-porous and highly durable.
- Hardness
- 7 Mohs
- Color
- Tan to off-white with minor iron staining
- Luster
- Dull/Waxy (weathered) to Vitreous (internal)
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Physical properties
Hardness: 7 Mohs; Color: Tan to off-white with minor iron staining; Luster: Dull/Waxy (weathered) to Vitreous (internal); Structure: Granular/Crystalline; Non-porous and highly durable.
Formation & geological history
Formed from the metamorphism of quartz sandstone under intense heat and pressure. This specimen shows significant rounding and smoothing due to fluvial (river) or glacial transport over thousands of years.
Uses & applications
Commonly used as a construction aggregate, in landscaping as river rock, and as a raw material for high-silica glass manufacture or metallurgical flux.
Geological facts
Quartzite is so durable that it often survives multiple cycles of erosion, remaining as pebbles long after the surrounding softer rocks have been ground into sand. It is harder than steel and cannot be scratched by a knife.
Field identification & locations
Identify in the field by its hardness (it will scratch glass) and its granular appearance which looks like sparkling sugar on a fresh break. Commonly found in riverbeds and glacial tills globally.
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