metamorphic
Quartzite
Quartzite (composed primarily of Silicon Dioxide, SiO2)
Hardness: 7 on Mohs scale; Color: Tan, brown, or grayish; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- Tan, brown, or grayish
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, brown, or grayish; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. Under intense heat and pressure, quartz grains recrystallize and fuse together, creating an extremely hard and durable rock.
Uses & applications
Used as crushed stone for road construction, railway ballast, and as a decorative stone in landscaping or architecture. In some cases, high-purity quartzite is used to produce silica sand for glassmaking.
Geological facts
Quartzite is so hard that it will scratch glass and steel. It is often more resistant to weathering than the surrounding rock, leading it to form prominent ridges and mountain peaks.
Field identification & locations
Identifiable in the field by its extreme hardness and grainy, sugary appearance on fresh surfaces. It is found globally in mountainous regions where ancient sedimentary basins have undergone tectonic squeezing.
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