metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: White, gray, or tan with dark mineral inclusions; Luster: Vitreous to dull; Crystal structure: Non-foliated, interlocking quartz grains; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- White, gray, or tan with dark mineral inclusions
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: White, gray, or tan with dark mineral inclusions; Luster: Vitreous to dull; Crystal structure: Non-foliated, interlocking quartz grains; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure, typically during mountain-building events. This specimen shows significant rounding from fluvial or glacial transport.
Uses & applications
Used as crushed stone for road construction, railway ballast, and as a decorative stone in landscaping. High-purity quartzite is used to produce silica sand for glassmaking and industrial abrasives.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during erosion, often forming the caps of ridges and mountains. It is significantly harder than the sandstone from which it originates.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass) and its sugary, crystalline texture. Common in metamorphic belts and as pebbles in riverbeds or beaches worldwide.
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