metamorphic

Quartzite (River Pebble)

Metamorphosed Quartz Sandstone (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale); Color: Tan, brown, or grayish with occasional reddish tints; Luster: Dull to vitreous; Crystal Structure: Granular/Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Hardness: 7 (Mohs scale)
Color: Tan, brown, or grayish with occasional reddish tints
Luster: Dull to vitreous

Identified February 22, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed through the regional metamorphism of quartz-rich sandstone subjected to extreme heat and pressure, causing the sand grains to recrystallize into a dense network. This specific specimen has been rounded and smoothed by water transport in a river or glacial environment.

Uses & applications

Used primarily as construction aggregate, road ballast, and in ornamental landscaping. High-purity quartzite is used in the glass and ceramic industries.

Geological facts

Quartzite is so durable that it often remains as resistant ridges or hills long after surrounding softer rocks have eroded away. It is often tougher than the sandstone from which it originated.

Field identification & locations

Identify in the field by its extreme hardness (it will easily scratch glass and stainless steel) and the way it breaks through sand grains rather than around them. Commonly found in riverbeds, glacial tills, and mountainous regions worldwide.