metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 (Mohs scale); Color: Tan, brown, or grayish; Luster: Vitreous to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal or irregular fracture); Specific Gravity: 2.6-2.7
- Hardness
- 7 (Mohs scale)
- Color
- Tan, brown, or grayish
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Tan, brown, or grayish; Luster: Vitreous to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal or irregular fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartz sandstone. Intense heat and pressure cause quartz grains to recrystallize and fuse together, eliminating the original pore spaces. It can form in various geological ages during mountain-building events.
Uses & applications
Used primarily in construction for crushed stone, road ballast, and building facades. Higher quality pieces are used as decorative gemstones in landscaping or simple lapidary work.
Geological facts
Quartzite is so durable that it often survives intense erosion to form the crests of ridges and hills. It is notably harder than the sandstone it originates from and will scratch glass easily.
Field identification & locations
Identify in the field by its extreme hardness and the fact that it breaks across the quartz grains rather than around them (unlike sandstone). Commonly found in ancient mountain ranges and glacial deposits.
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