metamorphic
Quartzite (River Cobble)
Quartzite (primarily SiO2)
Hardness: 7 (Mohs scale); Color: tan, white, buff with smoky grey patches; Luster: dull to waxy; Texture: grainy/saccharoidal; Cleavage: none (conchoidal fracture).
- Hardness
- 7 (Mohs scale)
- Color
- tan, white, buff with smoky grey patches
- Luster
- dull to waxy
Identified More metamorphic →
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Physical properties
Hardness: 7 (Mohs scale); Color: tan, white, buff with smoky grey patches; Luster: dull to waxy; Texture: grainy/saccharoidal; Cleavage: none (conchoidal fracture).
Formation & geological history
Formed through the metamorphism of quartz sandstone under high heat and pressure, typically during mountain-building events. This specific specimen has been further shaped and smoothed by water transport in a river or glacial environment.
Uses & applications
Used as crushed stone in construction, road ballast, and occasionally as an ornamental stone in landscaping or for lapidary tumbling.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the tops of ridges and mountains because it resists erosion better than the surrounding rocks.
Field identification & locations
Identify by its ability to scratch glass and its grainy texture that looks like sandpaper but feels smooth. Found globally in riverbeds and glacial tills. Collectors look for smooth, well-rounded shapes or unique color banding.
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