metamorphic
Quartzite pebble
Quartzite (SiO2)
Hardness: 7 (Mohs scale), Color: light greyish-blue to creamy white, Luster: vitreous to waxy, Crystal structure: Trigonal (microcrystalline), Cleavage: none (conchoidal fracture), Specific gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: light greyish-blue to creamy white, Luster: vitreous to waxy, Crystal structure: Trigonal (microcrystalline), Cleavage: none (conchoidal fracture), Specific gravity: 2.65
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure, where original quartz grains recrystallize into an interlocking mosaic of crystals. This specimen is water-worn into a rounded pebble.
Uses & applications
Primarily used in construction for crushed stone and railway ballast; decorative varieties are used in jewelry (as beads or cabochons) and as ornamental stones in landscaping.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during erosion, remaining as pebbles and boulders in riverbeds and on beaches for millions of years.
Field identification & locations
Identify by its hardness (it will easily scratch glass) and lack of visible grains compared to sandstone. Commonly found in riverbeds, glacial tills, and ancient mountain belts like the Appalachians or the Alps.
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