metamorphic

Quartzite Cobble

Quartzite (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: tan, grey, or off-white with localized iron staining; Luster: dull to vitreous; Texture: granoblastic with visible fused sand grains; Structure: massive and non-foliated.

Hardness: 7 on Mohs scale
Color: tan, grey, or off-white with localized iron staining
Luster: dull to vitreous

Identified July 13, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed from the metamorphism of quartz-rich sandstone subjected to extreme heat and pressure, typically during mountain-building events (orogeny). Rounded into cobbles by fluvial (river) or glacial transport over thousands of years.

Uses & applications

Commonly used in landscaping, road construction (as crushed aggregate), and occasionally as a refractory material in industrial furnaces due to high silica content.

Geological facts

Quartzite is so hard that it will scratch glass and even high-quality steel tools. It is one of the most physically durable and chemically resistant rocks found on Earth's surface.

Field identification & locations

Identify in the field by its hardness (will not scratch with a knife) and its grainy, sandpaper-like surface that nonetheless feels smooth due to water-wear; found abundantly in riverbeds and glacial tills.