metamorphic
Quartzite Pebble
Quartzite (SiO2)
Hardness: 7 (Mohs scale). Color: White, gray, brownish-tan. Luster: Vitreous to dull. Crystal structure: Trigonal (microcrystalline). Cleavage: None, exhibits conchoidal or irregular fracture. Specific gravity: 2.6-2.7.
- Hardness
- 7 (Mohs scale)
- Color
- White, gray, brownish-tan
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale). Color: White, gray, brownish-tan. Luster: Vitreous to dull. Crystal structure: Trigonal (microcrystalline). Cleavage: None, exhibits conchoidal or irregular fracture. Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure cause the original quartz grains to recrystallize and fuse together. This specific specimen has been further shaped and rounded by water erosion in a river or coastal environment.
Uses & applications
Commonly used in construction as aggregate, road ballast, or landscaping. High-purity quartzite is used in the glass industry and to produce silicon metal for electronics.
Geological facts
Quartzite is so hard and dense that when it breaks, the fracture passes through the quartz grains rather than along their boundaries, unlike its parent sandstone. It is one of the most durable rocks found on the Earth's surface.
Field identification & locations
Identified in the field by its extreme hardness (cannot be scratched by steel) and lack of reaction to acid. It often feels 'sandy' to the touch but has a sugary, crystalline look on a fresh break. Found worldwide in ancient mountain belts and river beds.
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