metamorphic
Quartzite River Cobble
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: Brownish-grey with weathering rind; Luster: Dull (weathered) to vitreous (broken surface); Crystal Structure: Granular/Microcrystalline; High specific gravity.
- Hardness
- 7 on Mohs scale
- Color
- Brownish-grey with weathering rind
- Luster
- Dull (weathered) to vitreous (broken surface)
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Physical properties
Hardness: 7 on Mohs scale; Color: Brownish-grey with weathering rind; Luster: Dull (weathered) to vitreous (broken surface); Crystal Structure: Granular/Microcrystalline; High specific gravity.
Formation & geological history
Formed from the metamorphism of quartz sandstone under intense heat and pressure, typically during mountain-building events. This specific specimen has been further shaped into a rounded cobble through fluvial erosion in a river environment.
Uses & applications
Used in construction as crushed stone or ballast; historically used for stone tools due to its hardness and conchoidal fracturing; commonly used in landscaping and as decorative river rock.
Geological facts
Quartzite is so durable that it often survives multiple cycles of erosion and sedimentation. It is tougher than the parent sandstone and will break through the quartz grains rather than around them.
Field identification & locations
Identify by its hardness (it will easily scratch glass) and its dense, granular texture. Commonly found in riverbeds, glacial deposits, and ancient metamorphic belts. It is one of the most resistant rocks to mechanical weathering.
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