metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale (scratches glass). Color: Grayish-white to tan. Luster: Vitreous to dull. Crystal structure: Hexagonal (microcrystalline/interlocked). Cleavage: None (conchoidal fracture). Specific gravity: 2.6 - 2.7.
- Hardness
- 7 on Mohs scale (scratches glass)
- Color
- Grayish-white to tan
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale (scratches glass). Color: Grayish-white to tan. Luster: Vitreous to dull. Crystal structure: Hexagonal (microcrystalline/interlocked). Cleavage: None (conchoidal fracture). Specific gravity: 2.6 - 2.7.
Formation & geological history
Formed through the metamorphism of quartz sandstone. High heat and pressure cause the quartz grains to recrystallize and fuse together, creating a very dense, tough rock. Most commonly formed during mountain-building events (orogenies).
Uses & applications
Used in construction as crushed stone or road ballast, as decorative stone in architecture (flooring, wall cladding), and historically for making stone tools due to its hardness and fracturing pattern.
Geological facts
Quartzite is so tough that it usually breaks through the quartz grains rather than around them, which is how it is distinguished from its parent rock, sandstone. It is often found capping hills or ridges because it is highly resistant to chemical and physical weathering.
Field identification & locations
Identify in the field by its extreme hardness and sugary or glassy texture on fresh breaks. It will scratch glass easily but will not react to acid. Found globally in ancient tectonic belts and Appalachian-type mountain ranges.
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