metamorphic
River Pebble (likely Quartzite or Quartz)
Quartzite (SiO2)
Hardness: 7 (Mohs scale); Color: Grayish-white to light blue; Luster: Vitreous to dull; Crystal structure: Hexagonal (trigonal); Grainy texture; High specific gravity.
- Hardness
- 7 (Mohs scale)
- Color
- Grayish-white to light blue
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Grayish-white to light blue; Luster: Vitreous to dull; Crystal structure: Hexagonal (trigonal); Grainy texture; High specific gravity.
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure. This specimen shows significant rounding and smoothing due to fluvial erosion in a river or coastal environment.
Uses & applications
Commonly used in construction as aggregate, in landscaping, and as decorative stones. Smooth river pebbles are popular in aquarium decor and Zen gardens.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during erosion, remaining as pebbles long after softer minerals have dissolved. It is frequently more durable than granite.
Field identification & locations
Identify in the field by its hardness (will scratch glass and steel) and its grainy, sandpaper-like texture that appears sugary under a magnifying glass. Found globally in riverbeds and glacial deposits.
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