metamorphic
Quartzite (River Stone)
Quartzite (mainly SiO2 with iron oxide staining)
Hardness: 7 (Mohs scale), Color: Brownish-tan due to iron staining, Luster: Vitreous to dull, Crystal structure: Trigonal/Hexagonal crystals fused together, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: Brownish-tan due to iron staining, Luster: Vitreous to dull, Crystal structure: Trigonal/Hexagonal crystals fused together, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz sandstone under high heat and pressure, causing sand grains to recrystallize into a dense network. This specific pebble was subsequently rounded by fluvial (river) erosion.
Uses & applications
Commonly used as decorative landscaping gravel, crushed stone for road construction, and occasionally as a source of silica for glass manufacturing.
Geological facts
Quartzite is so tough that it usually breaks through the quartz grains rather than around them. Rounded river stones like this are often called 'cobbles' and can travel hundreds of miles from their original source.
Field identification & locations
Identify in the field by its hardness (it can scratch glass) and its sugary, crystalline texture on a fresh break. Commonly found in riverbeds, glacial deposits, and sedimentary basins worldwide.
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