metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, often with yellow or tan staining from iron oxides; Luster: vitreous to dull; Crystal structure: trigonal (granular mosaic); Cleavage: none; Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Luster
- vitreous to dull
Identified More metamorphic →
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray, often with yellow or tan staining from iron oxides; Luster: vitreous to dull; Crystal structure: trigonal (granular mosaic); Cleavage: none; Specific gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone. High heat and pressure cause the quartz grains to recrystallize and fuse together, creating a dense, hard rock. Found in mountain ranges and ancient shield regions.
Uses & applications
Used as a decorative stone in construction, road ballast, railway track bedding, and sometimes as a source of silica for glassmaking. Small specimens are popular for amateur geology collections.
Geological facts
Quartzite is so hard that when it breaks, the fracture passes through the quartz grains rather than around them, which distinguishes it from sandstone. Some quartzite formations are over a billion years old.
Field identification & locations
Identified in the field by its extreme hardness (cannot be scratched by steel) and its crystalline, sugary texture. It is a common 'river rock' due to its resistance to weathering and abrasion.
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