metamorphic
Quartzite (clastic/metamorphic subtype)
Quartzite (primarily Silicon Dioxide, SiO2)
Hardness: 7 on Mohs scale; Color: Grayish-white with sugary texture; Luster: Vitreous to dull; Crystal structure: Hexagonal (microcrystalline/interlocking); Cleavage: None (conchoidal fracture); Specific gravity: 2.6 - 2.7
- Hardness
- 7 on Mohs scale
- Color
- Grayish-white with sugary texture
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Grayish-white with sugary texture; Luster: Vitreous to dull; Crystal structure: Hexagonal (microcrystalline/interlocking); Cleavage: None (conchoidal fracture); Specific gravity: 2.6 - 2.7
Formation & geological history
Formed from the metamorphism of quartz sandstone. Intense heat and pressure cause the original quartz grains to recrystallize and fuse together into a dense, hard rock. This specimen appears weathered/water-worn.
Uses & applications
Used primarily in construction for road ballast, railway tracks, and decorative landscaping. High-purity quartzite is used to produce silica sand for glassmaking and industrial abrasives.
Geological facts
Quartzite is so tough that it often survives where other rocks weather away, forming the caps of ridges and mountains. It is harder than steel and will easily scratch glass and pocket knives.
Field identification & locations
Identify in the field by its 'sugary' texture and extreme hardness (it will scratch glass). Often found in areas of tectonic activity where ancient sedimentary basins were compressed. Common in glacial till or riverbeds.
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