metamorphic
Quartzite (River-worn pebble)
Quartzite (Mainly SiO2)
Hardness: 7 on Mohs scale; Color: Grayish-tan/off-white with subtle translucency; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Grayish-tan/off-white with subtle translucency
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Grayish-tan/off-white with subtle translucency; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure Recrystallize the sand grains into a dense, interlocking mosaic of quartz. This specific specimen has been rounded by fluvial (river) erosion over thousands of years.
Uses & applications
Used as aggregate in construction, road ballast, and decorative landscaping. High-purity quartzite is used in the glass and metallurgy industry. Small pebbles like this are often kept as pocket stones or used in rock tumblers.
Geological facts
Quartzite is so durable that it can survive long-distance transport in rivers and glacial meltwater that would destroy most other rocks. It is often harder than the steel files used to test it.
Field identification & locations
Identify in the field by its hardness (it will easily scratch glass) and lack of visible grains compared to sandstone. It often has a 'sugary' texture on fresh breaks. Very common in riverbeds and mountainous regions globally.
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