metamorphic
Quartzite
Quartzite (Primary mineral: Silicon Dioxide, SiO₂)
Hardness: 7 on Mohs scale (scratches glass); Color: Off-white, tannish, or gray; Luster: Vitreous to dull; Crystal structure: Non-foliated, granoblastic; Cleavage: None (conchoidal fracture); Specific gravity: 2.6–2.7.
- Hardness
- 7 on Mohs scale (scratches glass)
- Color
- Off-white, tannish, or gray
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale (scratches glass); Color: Off-white, tannish, or gray; Luster: Vitreous to dull; Crystal structure: Non-foliated, granoblastic; Cleavage: None (conchoidal fracture); Specific gravity: 2.6–2.7.
Formation & geological history
Formed through the regional metamorphism of quartzose sandstone. Under intense heat and pressure, original quartz grains recrystallize and fuse together, creating a hard, interlocking network. It can originate from any geological age where sandstone was present.
Uses & applications
Used extensively in construction as crushed stone for road gravel and railway ballast. Due to its durability and resistance to weathering, it is used for floor tiles, decorative wall coverings, and countertops. It is also a source of silica for glassmaking.
Geological facts
Quartzite is so tough that it often fractures across the original grains rather than around them, unlike its parent rock sandstone. In the stone age, it was occasionally used as a substitute for flint to create stone tools, although it is more difficult to flake.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and its grainy, crystalline texture that looks like boiled sugar. It is commonly found in mountainous regions or ancient shield areas where tectonic activity occurred. Collectors look for pieces with interesting mineral inclusions or mineral staining.
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