metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: Gray, white, or brown with possible iron staining; Luster: Vitreous to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Gray, white, or brown with possible iron staining
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, white, or brown with possible iron staining; Luster: Vitreous to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure, typically during mountain-building events (orogeny). The individual quartz grains recrystallize into a locked mosaic.
Uses & applications
Used in construction as crushed stone for road aggregate, as decorative stone in landscaping, and historically for stone tools due to its hardness and durability.
Geological facts
Quartzite is so hard that it will scratch glass and even high-quality steel tools. Because of its resistance to weathering, it often forms the ridges and peaks of mountain ranges.
Field identification & locations
Identify in the field by its grainy, sugary texture and extreme hardness. It is commonly found in metamorphic terranes worldwide, such as the Appalachian Mountains or the Alps. It lacks the fizzes response to acid that limestone has.
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