metamorphic
Yellow Quartzite (River Cobble)
Quartzite (mainly SiO2)
Hardness: 7 (Mohs scale); Color: Yellow to tan with white streaks; Luster: Vitreous to waxy when wet; Structure: Granular/crystalline; Cleavage: None (conchoidal fracture); SG: ~2.65
- Hardness
- 7 (Mohs scale)
- Color
- Yellow to tan with white streaks
- Luster
- Vitreous to waxy when wet
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Physical properties
Hardness: 7 (Mohs scale); Color: Yellow to tan with white streaks; Luster: Vitreous to waxy when wet; Structure: Granular/crystalline; Cleavage: None (conchoidal fracture); SG: ~2.65
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure Recrystallized the sand grains into a dense, interlocking matrix. This specific specimen has been rounded and smoothed by water transport in a river or beach environment.
Uses & applications
Used as decorative stone in landscaping, crushed for road ballast, or as a source of silica in glass manufacturing. Smooth river stones are popular in massage therapy and rock painting.
Geological facts
Quartzite is so tough that it usually fractures through the original sand grains rather than around them, which distinguishes it from sandstone. This specimen likely owes its yellow color to trace amounts of iron oxide (limonite/hematite) staining.
Field identification & locations
Identify in the field by its inability to be scratched by a steel knife (H=7) and its sugary, granular texture. It will not fizz when exposed to acid, unlike limestone. Common in glacial till and river beds.
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