metamorphic
Quartzite
Metamorphosed Quartz Sandstone (SiO2)
Hardness: 7 (Mohs scale); Color: White to light gray; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal crystals within a granular matrix; Specific Gravity: 2.6-2.7
- Hardness
- 7 (Mohs scale)
- Color
- White to light gray
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: White to light gray; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal crystals within a granular matrix; Specific Gravity: 2.6-2.7
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone under intense heat and pressure, typically during mountain-building events. The original quartz grains recrystallize into a dense interlaced network.
Uses & applications
Used in construction for road ballast, floor tiles, and countertop slabs. High-purity quartzite is also used to produce silica sand for glassmaking and industrial abrasives.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rock layers, forming spectacular ridges and mountain peaks in many geological ranges. It is harder than steel and will scratch a glass plate easily.
Field identification & locations
Identify in the field by its sugary texture and extreme hardness (it will not be scratched by a steel nail). Look for it in glaciated riverbeds or mountain outcroppings. Common in the Appalachian Mountains and the Great Lakes region.
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