metamorphic
Quartzite / Chert Pebble
Metamorphic Quartzite (primarily SiO2) with iron-oxide staining
AI-generated identification · may be incorrectHardness: 7 on Mohs scale; Color: tan, grey, cream with peach-orange iron oxide staining; Luster: dull to waxy/greasy; Crystal system: Trigonal (microcrystalline to granoblastic); Cleavage: none, breaks with conchoidal to sub-conchoidal fracture; Specific Gravity: ~2.65
- Hardness
- 7 on Mohs scale
- Color
- tan, grey, cream with peach-orange iron oxide staining
- Luster
- dull to waxy/greasy
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Physical properties
Hardness: 7 on Mohs scale; Color: tan, grey, cream with peach-orange iron oxide staining; Luster: dull to waxy/greasy; Crystal system: Trigonal (microcrystalline to granoblastic); Cleavage: none, breaks with conchoidal to sub-conchoidal fracture; Specific Gravity: ~2.65
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone (or as a chert nodule), subjected to intense heat and pressure that fused the quartz grains, subsequently eroded and stream-rounded by fluvial transport.
Uses & applications
Used widely as construction aggregate, railway ballast, riprap, and raw material for silica manufacturing. Dense, well-rounded river pebbles are also used in lapidary tumbling and landscape decoration.
Geological facts
Quartzite is so durable that during fracturing, it breaks across the constituent quartz grains rather than along grain boundaries like its parent rock, sandstone. It often survives extensive river transport that destroys softer minerals.
Field identification & locations
Easily identified by its inability to be scratched by a steel blade or pocketknife (hardness 7), granular quartz texture, rounded irregular weathering rinds, and resistance to acid. Abundant in gravel bars, river beds, and glacial till deposits.
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