metamorphic
Quartzite Pebble
Metamorphosed Quartz Sandstone (SiO2)
Hardness: 7 (Mohs), Color: Tan to yellowish-brown, Luster: Vitreous to dull, Crystal Structure: Trigonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.63-2.65
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Physical properties
Hardness: 7 (Mohs), Color: Tan to yellowish-brown, Luster: Vitreous to dull, Crystal Structure: Trigonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.63-2.65
Formation & geological history
Formed when quartz-rich sandstone is subjected to high heat and pressure, causing the original quartz grains to recrystallize and fuse together. This specimen is a rounded river pebble shaped by water erosion.
Uses & applications
Used as decorative landscaping stone, in construction aggregates, and occasionally as a source of silica for glassmaking. Smooth pebbles are popular for meditation and home decor.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during erosion, often ending up as smooth cobbles in riverbeds. It is harder than a steel knife and will easily scratch glass.
Field identification & locations
Field identification involves testing for hardness (cannot be scratched by steel) and lack of reaction to acid. Commonly found in riverbeds, glacial deposits, and mountain ranges globally.
