metamorphic
Quartzite Pebble
Metamorphosed Quartz Sandstone (SiO2)
Hardness: 7 on the Mohs scale; Color: Brown to reddish-brown due to iron oxide staining; Luster: Vitreous to greasy on fractured surfaces; Crystal structure: Trigonal (microcrystalline quartz grains fused together); Cleavage: None, breaks with a conchoidal fracture; Specific Gravity: 2.65.
- Hardness
- 7 on the Mohs scale
- Color
- Brown to reddish-brown due to iron oxide staining
- Luster
- Vitreous to greasy on fractured surfaces
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Physical properties
Hardness: 7 on the Mohs scale; Color: Brown to reddish-brown due to iron oxide staining; Luster: Vitreous to greasy on fractured surfaces; Crystal structure: Trigonal (microcrystalline quartz grains fused together); Cleavage: None, breaks with a conchoidal fracture; Specific Gravity: 2.65.
Formation & geological history
Formed from quartz-rich sandstone that has been subjected to intense heat and pressure (metamorphism), typically during tectonic mountain-building events. The original quartz grains recrystallize and fuse tightly with a quartz cement, making the rock extremely durable and resistant to weathering.
Uses & applications
Used in construction as road aggregate, railroad ballast, and dimension stone, as well as in manufacturing refractories and silica brick.
Geological facts
Because quartzite is harder than steel and extremely resistant to chemical weathering, sandstones that undergo this metamorphism often survive as prominent ridges and mountains while softer surrounding rocks erode away.
Field identification & locations
Found worldwide in metamorphic belts and commonly as water-worn pebbles in riverbeds and beaches due to its extreme durability. It can be identified by its inability to be scratched by steel and its refusal to effervesce with hydrochloric acid.
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