metamorphic
Quartzite Pebble (River Rock)
Quartzite (mainly SiO2)
Hardness: 7 (Mohs scale); Color: Tan, yellowish-white, or off-white; Luster: Vitreous to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6 - 2.7.
- Hardness
- 7 (Mohs scale)
- Color
- Tan, yellowish-white, or off-white
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Tan, yellowish-white, or off-white; Luster: Vitreous to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6 - 2.7.
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone under intense heat and pressure. This specific specimen is a 'river rock,' meaning it was physically weathered and rounded by water transport in a fluvial environment.
Uses & applications
Used in landscaping, construction (aggregate), high-purity silica for glassmaking, and frequently collected as 'worry stones' or for rock tumbling.
Geological facts
Quartzite is so hard that it will scratch glass and even steel. It is more durable than its parent rock, sandstone, because the quartz grains have fused together into a solid crystalline mass.
Field identification & locations
Identify in the field by its hardness (cannot be scratched by a steel nail) and grainy, sugary texture visible on fresh surfaces despite the smooth, water-worn exterior. Found globally in riverbeds and glacial deposits.
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