metamorphic
Quartzite River Cobble
Quartzite (dominated by SiO2)
Hardness: 7 (Mohs scale); Color: Tan, grey, and buff with a thin iron-stained vein; Luster: Dull/earthy (weathered); Crystal structure: Granoblastic (granular); Cleavage: None (fractures across grains); Specific gravity: 2.6-2.7
- Hardness
- 7 (Mohs scale)
- Color
- Tan, grey, and buff with a thin iron-stained vein
- Luster
- Dull/earthy (weathered)
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Physical properties
Hardness: 7 (Mohs scale); Color: Tan, grey, and buff with a thin iron-stained vein; Luster: Dull/earthy (weathered); Crystal structure: Granoblastic (granular); Cleavage: None (fractures across grains); Specific gravity: 2.6-2.7
Formation & geological history
Originally formed as quartz-rich sandstone (sedimentary) through deposition, then subjected to intense heat and pressure (metamorphism) which fused the sand grains together. This specific specimen was later tumbled and rounded by water action in a river or glacial environment.
Uses & applications
Primarily used as a decorative stone in landscaping, as a construction aggregate, or as a paperweight/collectible souvenir due to its pleasing rounded shape.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during erosion. The thin reddish line across this specimen is likely a fracture filled with iron oxide (limonite or hematite).
Field identification & locations
Identify in the field by its sugary, granular texture and extreme hardness (it will easily scratch glass). Rounded specimens like this are common in riverbeds, glacial tills, and alluvial fans worldwide.
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