metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: White to light gray; Luster: Vitreous to dull; Crystal structure: Non-foliated, granular; Cleavage: None, breaks with conchoidal fracture; Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- White to light gray
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: White to light gray; Luster: Vitreous to dull; Crystal structure: Non-foliated, granular; Cleavage: None, breaks with conchoidal fracture; Specific gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz sandstone under high heat and pressure. This process causes the individual quartz grains to recrystallize and fuse together, creating an extremely hard and durable rock found in various mountain ranges worldwide.
Uses & applications
Used in construction as crushed stone for road bases or railroad ballast, as dimension stone for wall coverings and flooring, and in glass manufacturing if the quartz purity is high enough.
Geological facts
Quartzite is so hard and chemically resistant that it often forms prominent ridges and hills, as it resists weathering more effectively than the surrounding rocks like limestone or shale.
Field identification & locations
Identify it by its extreme hardness (cannot be scratched by steel) and its grainy, sandpaper-like texture that doesn't rub off. It is commonly found in metamorphic terranes and riverbeds downstream from mountain ranges. Collectors look for unique colors or embedded crystals.
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