metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale. Color: White to grey, sometimes yellowish or brownish. Luster: Vitreous to greasy. Crystal structure: Trigonal (microcrystalline). Cleavage: None; displays conchoidal fracture. Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- White to grey, sometimes yellowish or brownish
- Luster
- Vitreous to greasy
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Physical properties
Hardness: 7 on Mohs scale. Color: White to grey, sometimes yellowish or brownish. Luster: Vitreous to greasy. Crystal structure: Trigonal (microcrystalline). Cleavage: None; displays conchoidal fracture. Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. Under high heat and pressure, quartz grains recrystallize and fuse together. It is found in mountain belts and Precambrian shield areas worldwide.
Uses & applications
Used as crushed stone for road construction, railroad ballast, and building stone. High-purity quartzite is used to produce glass, ferrosilicon, and silicon metal. It is also used for countertops and floor tiles.
Geological facts
Quartzite is so tough that it often creates prominent ridges and hilltops because it resists weathering more effectively than surrounding rocks. It is often confused with marble, but can be distinguished because quartzite will scratch glass while marble will not.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and its grainy, sandpaper-like texture that sparkles in the light. It is commonly found in the Appalachian Mountains, the Alps, and the Lake Superior region.
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