Metamorphic (low-grade)

Grey River Stone (Quartz-rich Quartzite/Siltstone)

Quartzite / Meta-siltstone (primarily SiO2)

AI-generated identification · may be incorrect

Hardness: 6-7 on Mohs scale; Color: Grey with slight blueish undertones and white specks; Luster: Dull to waxy; Structure: Finely crystalline, non-foliated to weakly foliated; Specific Gravity: Approx 2.6

Hardness: 6-7 on Mohs scale
Color: Grey with slight blueish undertones and white specks
Luster: Dull to waxy

Identified March 28, 2026More metamorphic (low-grade) →

Explore Grey River Stone (Quartz-rich Quartzite/Siltstone) in the encyclopedia →

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Physical properties

Formation & geological history

Formed from the metamorphism of quartz-rich sedimentary rocks (like sandstone or siltstone) under intense heat and pressure. This specific specimen has been further shaped and smoothed by fluvial or alluvial processes (water erosion) over thousands of years.

Uses & applications

Used primarily as decorative landscaping stone, railroad ballast, or aggregate in construction. High-purity quartzite is also used to produce silica sand for glassmaking.

Geological facts

River stones like this are 'geological survivors'; their high quartz content makes them resistant to chemical weathering, allowing them to travel hundreds of miles down river systems while smaller, softer minerals dissolve.

Field identification & locations

Identify in the field by its hardness (it will scratch glass) and its smooth, rounded 'water-worn' appearance. Commonly found in riverbeds, glacial tills, and beaches. Collectors value them for rock tumbling or decorative mulch.