metamorphic
Quartzite Pebble
Quartzite (chiefly SiO2)
Hardness: 7 on Mohs scale; Color: Off-white to light tan; Luster: Vitreous to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Off-white to light tan
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Off-white to light tan; Luster: Vitreous to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone. High heat and pressure causes recrystallization of the sand grains into a dense, interlocking mosaic of quartz crystals. This specimen shows significant rounding from fluvial (river) or beach erosion.
Uses & applications
Used as an abrasive, in construction as crushed stone or decorative landscaping gravel, and as a source of silica for glass manufacturing.
Geological facts
Quartzite is so tough that it often outlasts the mountain ranges in which it forms, ending up as rounded pebbles in younger sedimentary basins. It is often harder than the steel blade of a knife.
Field identification & locations
Identify in the field by its hardness (will scratch glass easily) and granular texture that looks like sandpaper but feels smooth due to the interlocking crystals. Found globally in ancient mountain belts and riverbeds.
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