metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, brownish-gray, translucent; Luster: Vitreous to waxy; Crystal structure: Trigonal (microcrystalline); Cleavage: None, exhibits conchoidal or granular fracture; Specific gravity: 2.63 - 2.65
- Hardness
- 7 on Mohs scale
- Color
- Tan, brownish-gray, translucent
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, brownish-gray, translucent; Luster: Vitreous to waxy; Crystal structure: Trigonal (microcrystalline); Cleavage: None, exhibits conchoidal or granular fracture; Specific gravity: 2.63 - 2.65
Formation & geological history
Formed from the metamorphism of quartz sandstone. The original sand grains are recrystallized and fused together by heat and pressure during mountain-building events. Geological age varies widely by region.
Uses & applications
Used extensively in construction as crushed stone for road beds and railway ballast. Also used as dimension stone for counter tops and floor tiles due to its extreme durability.
Geological facts
Quartzite is so strong that when it breaks, it fractures through the individual sand grains rather than around them, distinguishing it from sandstone. It is resistant to chemical weathering.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by steel) and lack of reaction to acid. Often found in mountain ranges or as erosion-resistant pebbles in riverbeds. For collectors, look for pieces with interesting color banding.
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