metamorphic
Quartzite (River Cobble)
Quartzite (primarily SiO2)
Hardness: 7 (Mohs scale); Color: Grayish-brown with pinkish undertones; Luster: Dull to vitreous; Crystal structure: Non-foliated, interlocking quartz grains; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 (Mohs scale)
- Color
- Grayish-brown with pinkish undertones
- Luster
- Dull to vitreous
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Physical properties
Hardness: 7 (Mohs scale); Color: Grayish-brown with pinkish undertones; Luster: Dull to vitreous; Crystal structure: Non-foliated, interlocking quartz grains; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone under intense heat and pressure. This specific specimen has been Rounded by fluvial (river) or glacial transport, likely originating from ancient mountain belts and deposited in younger sedimentary layers.
Uses & applications
Commonly used as crushed stone for road construction, railway ballast, and as a decorative landscaping stone. High-purity quartzite is used to produce ferrosilicon and industrial silica sand.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the 'backbone' of mountain ranges. It is tougher than several types of steel, which is why it rapidly dulls tools used to cut it.
Field identification & locations
Identify in the field by its inability to be scratched by a steel knife and its sugary, crystalline texture when freshly broken. Found globally in riverbeds, glacial tills, and mountainous metamorphic terrains.
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