metamorphic
Quartzite
Quartzite (Mainly SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, may be pinkish; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6–2.7
- Hardness
- 7 on Mohs scale
- Color
- typically white to gray, may be pinkish
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray, may be pinkish; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6–2.7
Formation & geological history
Formed through the regional metamorphism of quartz sandstone. Under high heat and pressure, the individual quartz grains recrystallize and fuse together into a dense, crystalline mass. It can range in age from Precambrian to more recent metamorphic events.
Uses & applications
Used extensively as crushed stone for road construction, railway ballast, and as a decorative building stone. It is also used in the manufacturing of glass and ceramics due to its high silica content.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during erosion, frequently forming the peaks of mountains and ridges. It is often confused with marble, but unlike marble, quartzite will not fizz in contact with weak acids like vinegar.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass and steel) and its granular, sandpaper-like texture that does not rub off. Common in mountain ranges and metamorphic belts globally. Collectors look for high-purity white or vibrant colored specimens.
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