metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: Gray, tan, white, or light brown; Luster: Vitreous to dull; Crystal structure: Non-foliated, interlocking quartz grains; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Gray, tan, white, or light brown
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, tan, white, or light brown; Luster: Vitreous to dull; Crystal structure: Non-foliated, interlocking quartz grains; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. High heat and pressure cause the original quartz grains to recrystallize and fuse together. It can be found in mountain belts and Precambrian shields worldwide.
Uses & applications
Used as aggregate in road construction, railroad ballast, and building stone. Because of its hardness, it is also used as a decorative stone, in glass manufacturing, and as a refractory material.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rock layers during erosion, frequently forming the peaks of ridges and mountains. It is distinct from sandstone because it breaks across the grains rather than around them.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass and stainless steel) and the way it breaks through the mineral grains. Common in eroded mountain ranges and glacial deposits.
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