metamorphic
River Cobble (Quartzite with Iron Staining)
Metamorphic Quartzite (SiO2 with Fe2O3 inclusions)
Hardness: 7 (Mohs scale), Color: Cream/grey with reddish-brown oxidation, Luster: Dull to vitreous, Crystal Structure: Granoblastic, Cleavage: None/Conchoidal fracture, Specific Gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: Cream/grey with reddish-brown oxidation, Luster: Dull to vitreous, Crystal Structure: Granoblastic, Cleavage: None/Conchoidal fracture, Specific Gravity: 2.6-2.7
Formation & geological history
Originally formed as quartz sandstone, this specimen underwent intense heat and pressure (metamorphism) to fuse grains into quartzite. The rounded shape indicates significant transport by water (glacial or fluvial) during the Quaternary period.
Uses & applications
Used primarily as decorative landscaping stone, aggregate in construction, and low-cost material for rock tumbling. High-purity quartzite is used in glassmaking.
Geological facts
The reddish-brown 'veining' is caused by iron oxide (rust) leaching into fractures or porous areas of the rock. Quartzite is often tougher than its parent sandstone, making it highly resistant to physical weathering.
Field identification & locations
Identify in the field by its hardness (it will scratch glass) and rounded, water-worn surface. Commonly found in riverbeds, glacial tills, and decorative gardens across North America and Europe.
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