metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: Gray, white, or greenish-gray (due to impurities); Luster: Vitreous to waxy; Structure: Granoblastic/Non-foliated; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Gray, white, or greenish-gray (due to impurities)
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, white, or greenish-gray (due to impurities); Luster: Vitreous to waxy; Structure: Granoblastic/Non-foliated; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure cause quartz grains to recrystallize and fuse into a dense, interlocking network of crystals.
Uses & applications
Used as crushed stone for road construction, railroad ballast, and decorative building stone. Higher quality varieties are used for countertops or as semi-precious stones in lapidary.
Geological facts
Quartzite is so tough that it often breaks through the individual quartz grains rather than around them, which distinguishes it from sandstone. Many mountain ranges, such as parts of the Appalachians, are capped by resistant quartzite layers.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by steel) and lack of reaction to acid. It typically displays a sugary texture on fresh surfaces. Commonly found in folded mountain belts and ancient cratons.
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