metamorphic
Quartzite
Quartzite (SiO2-rich metamorphic rock)
Hardness: 7 on Mohs scale; Color: typically white to gray, often with earthy tan or brown staining; Luster: vitreous to dull; Crystal structure: granular, non-foliated; Cleavage: none (conchoidal fracture).
- Hardness
- 7 on Mohs scale
- Luster
- vitreous to dull
Identified More metamorphic →
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray, often with earthy tan or brown staining; Luster: vitreous to dull; Crystal structure: granular, non-foliated; Cleavage: none (conchoidal fracture).
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone under intense heat and pressure. This specimen shows significant rounding, indicating it was likely transported and smoothed in a riverbed or glacial environment.
Uses & applications
Commonly used as crushed stone in road construction, as railroad ballast, and for architectural stone. Higher purity varieties are used to produce silica sand for glassmaking.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during erosion, frequently forming the tops of ridges and resistant hills. It is often confused with marble, but can be distinguished because it will not react with acid and can scratch glass.
Field identification & locations
Identified in the field by its sugary texture and extreme hardness. It won't be scratched by a steel knife. It is found globally, common in ancient mountain belts and river gravel deposits.
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