metamorphic
Quartzite
Metamorphosed Quartz Sandstone (SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan (iron inclusions can cause yellow/orange staining as seen here); Luster: vitreous to dull; Crystal structure: hexagonal precursor minerals fused into a granular, interlocking mosaic; Cleavage: none (conchoidal fracture).
- Hardness
- 7 on Mohs scale
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan (iron inclusions can cause yellow/orange staining as seen here); Luster: vitreous to dull; Crystal structure: hexagonal precursor minerals fused into a granular, interlocking mosaic; Cleavage: none (conchoidal fracture).
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. High heat and pressure cause the individual sand grains to recrystallize and fuse together, losing the original porous texture. It can be found in mountain belts and Precambrian shields globally.
Uses & applications
Used extensively in construction as crushed stone for road beds, railway ballast, and riprap. Smooth variations are used for flooring, countertops, and decorative masonry. Due to its silica content, it is also used in the manufacture of glass and abrasives.
Geological facts
Quartzite is so tough that it often resists weathering more effectively than the surrounding rocks, frequently forming the tops of ridges and mountain peaks. Unlike sandstone, which breaks around the grains, quartzite breaks through the sand grains due to their complete fusion.
Field identification & locations
Identify it by its extreme hardness (it will easily scratch glass and stainless steel) and the way it breaks through the grains rather than around them. It is commonly found in gravel pits, eroded riverbeds, and ancient glaciated terrains.
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