metamorphic
Quartzite (River Pebble)
Meta-quartzite (composed primarily of SiO2)
Hardness: 7 on Mohs scale; Color: grayish-white; Luster: vitreous to dull (when weathered); Crystal structure: non-foliated, granular; Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- grayish-white
- Luster
- vitreous to dull (when weathered)
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Physical properties
Hardness: 7 on Mohs scale; Color: grayish-white; Luster: vitreous to dull (when weathered); Crystal structure: non-foliated, granular; Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone subjected to high heat and pressure. This specific specimen has been further shaped by fluvial erosion (water transport), resulting in its rounded, smooth pebble shape.
Uses & applications
Used as a high-durability construction aggregate, in railway ballast, for manufacturing glass (if high purity), and in ornamental landscaping/garden design.
Geological facts
Quartzite is so hard that it will scratch glass and even steel. It is one of the most chemically and physically resistant rocks found on Earth's surface, often outlasting the surrounding mountains from which it originated.
Field identification & locations
Identify in the field by its inability to be scratched by a steel knife, its sugary/crystalline texture when broken, and lack of reaction to acid. Commonly found in riverbeds, glacial tills, and ancient mountain belts like the Appalachians or the Alps.
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