metamorphic
Quartzite
Quartzite (Mainly SiO2)
Hardness: 7 on Mohs scale (scratches glass). Color: White, gray, or tan. Luster: Vitreous to dull. Crystal structure: Granular, non-foliated. Texture: Sugary or sandpaper-like appearance but feels smooth upon break. Specific Gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale (scratches glass)
- Color
- White, gray, or tan
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale (scratches glass). Color: White, gray, or tan. Luster: Vitreous to dull. Crystal structure: Granular, non-foliated. Texture: Sugary or sandpaper-like appearance but feels smooth upon break. Specific Gravity: 2.6-2.7.
Formation & geological history
Quartzite forms through the metamorphism of quartz-rich sandstone. High heat and pressure cause the quartz grains to recrystallize and fuse together. It is commonly found in mountain belts and Precambrian shields.
Uses & applications
Used extensively in road construction, as railroad ballast, for kitchen countertops (due to its durability), and as a decorative stone in architecture. High-purity quartzite is used to produce glass and metallic silicon.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rock in weathering processes, forming prominent ridges or mountain peaks. Unlike sandstone, when quartzite breaks, it breaks across the quartz grains rather than around them.
Field identification & locations
Identify by its extreme hardness and sugary texture. It will not fizz with acid (unlike limestone/marble) and cannot be scratched by a steel knife. Common in ancient mountain ranges like the Appalachians or the Alps.
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