metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, often with yellow or tan tinges; Luster: vitreous or dull; Crystal structure: Trigonal (microcrystalline); Cleavage: missing (breaks with conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- typically white to gray, often with yellow or tan tinges
- Luster
- vitreous or dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray, often with yellow or tan tinges; Luster: vitreous or dull; Crystal structure: Trigonal (microcrystalline); Cleavage: missing (breaks with conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure, typically during mountain-building events. The original quartz grains recrystallize and fuse together.
Uses & applications
Used in construction as crushed stone for road gravel and rail ballast, as decorative stone in architecture and flooring, and occasionally in glassmaking if pure enough.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rock in the landscape, forming the tops of ridges and mountains. It is significantly harder than the sandstone it originates from.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass) and its sugary, crystalline appearance on fresh surfaces. It is ubiquitous in shield areas and folded mountain belts.
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