metamorphic
Quartzite Pebble
Metamorphosed Quartz Sandstone
Hardness: 7 (Mohs scale); Color: light grey with yellowish-tan weathering; Luster: dull to vitreous; Crystal structure: granular/microcrystalline; Cleavage: none; Specific gravity: approx. 2.65
- Hardness
- 7 (Mohs scale)
- Color
- light grey with yellowish-tan weathering
- Luster
- dull to vitreous
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Physical properties
Hardness: 7 (Mohs scale); Color: light grey with yellowish-tan weathering; Luster: dull to vitreous; Crystal structure: granular/microcrystalline; Cleavage: none; Specific gravity: approx. 2.65
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure cause quartz grains to recrystallize and fuse together. Often rounded into pebbles by water erosion in rivers or coastal environments.
Uses & applications
Primarily used in construction as crushed stone or ballast; exceptionally pure quartzite is used in glass making. Some colorful varieties are used as decorative garden stones.
Geological facts
Quartzite is so strong that when it breaks, it fractures through the quartz grains rather than along the boundaries between them, unlike its parent rock, sandstone.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel knife) and its grainy, sugary appearance. Commonly found in riverbeds and glacial deposits globally.
