metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 (Mohs scale); Color: Gray, tan, white, reddish; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None; Specific Gravity: 2.6 - 2.7
- Hardness
- 7 (Mohs scale)
- Color
- Gray, tan, white, reddish
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Gray, tan, white, reddish; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None; Specific Gravity: 2.6 - 2.7
Formation & geological history
Formed through the regional or contact metamorphism of quartzose sandstone. Under intense heat and pressure, quartz grains recrystallize and fuse together, creating a dense, hard rock.
Uses & applications
Used in construction as road metal, railway ballast, and decorative stone. Historically used for making stone tools (lithics) due to its conchoidal fracture. Sometimes used as flooring or countertops.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the caps of ridges and mountains because it resists erosion better than surrounding rocks. It can be distinguished from sandstone because it fractures through the grains rather than around them.
Field identification & locations
Identify by its extreme hardness (scratches glass/steel) and sugary, granular texture. Commonly found in folded mountain belts and ancient cratons worldwide. Does not react with acid, unlike marble.
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