metamorphic

Quartzite River Rock

Quartzite (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale), Color: Red-brown to purple due to iron oxide, Luster: Dull to waxy, Crystal Structure: Trigonal (granular), Cleavage: None, Specific Gravity: 2.6-2.7

Identified July 6, 2026More metamorphic →

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Physical properties

Hardness: 7 (Mohs scale), Color: Red-brown to purple due to iron oxide, Luster: Dull to waxy, Crystal Structure: Trigonal (granular), Cleavage: None, Specific Gravity: 2.6-2.7

Formation & geological history

Formed from the metamorphism of quartz sandstone under high heat and pressure. This specimen has been rounded and smoothed by water erosion (alluvial process) over thousands of years.

Uses & applications

Commonly used in landscaping, as railroad ballast, or crushed for construction aggregate. High-purity quartzite is used to produce silica sand for glass making.

Geological facts

Quartzite is so tough that it often survives intense glacial and fluvial transport where other rocks would crumble. It is harder than steel and will easily scratch glass.

Field identification & locations

Identify by its hardness (will scratch a knife blade) and granular 'sugary' texture. Commonly found in riverbeds, glacial tills, and ancient mountain belts.