metamorphic
Quartzite (River-worn Cobble)
Quartzite (composed primarily of SiO2)
Hardness: 7 (Mohs scale), Color: Reddish-brown/Maroon with white quartz veins, Luster: Vitreous to waxy (when polished), Crystal structure: Granular/Microcrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: Reddish-brown/Maroon with white quartz veins, Luster: Vitreous to waxy (when polished), Crystal structure: Granular/Microcrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure Recrystallize the quartz grains, locking them into a dense, hard mass. This specimen has been rounded and smoothed by water transport in a river or beach environment.
Uses & applications
Used as a high-quality railway ballast, construction aggregate, and in landscaping. Polished stones like these are often used as 'worry stones' or decorative garden pebbles.
Geological facts
Quartzite is so tough that it often outlasts the mountain ranges it formed in, remaining as resistant peaks or durable 'erratics' transported by glaciers across thousands of miles.
Field identification & locations
Identify by its extreme hardness; it will easily scratch glass and cannot be scratched by a steel knife. Look for the granular texture and lack of layering compared to sandstone. Common in glacial till and ancient riverbeds.
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