metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 (Mohs scale); Color: White to tan/grey; Luster: Vitreous to dull; Crystal structure: Trigonal (granular texture); Cleavage: None; Specific gravity: 2.6–2.7.
- Hardness
- 7 (Mohs scale)
- Color
- White to tan/grey
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: White to tan/grey; Luster: Vitreous to dull; Crystal structure: Trigonal (granular texture); Cleavage: None; Specific gravity: 2.6–2.7.
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure cause the quartz grains to recrystallize and fuse together. It can be found in mountain belts globally, often dating from the Precambrian to younger tectonic events.
Uses & applications
Used in construction for road ballast, floor tiles, and countertop surfaces. Also used as a decorative stone in landscaping and as a raw material for glass and ceramics due to its high silica content.
Geological facts
Quartzite is so hard that it will scratch glass and even some steel blades. When it breaks, the fracture passes through the quartz grains rather than around them, distinguishing it from sandstone.
Field identification & locations
Identify in the field by its sugary texture and extreme hardness (cannot be scratched by a knife). Commonly found in folded mountain ranges. Collectors look for pieces with interesting mineral inclusions or vibrant colors caused by iron oxides.
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