metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: Pink, white, or grey; Luster: Vitreous to dull; Crystal structure: Non-foliated granoblastic; Cleavage: None (breaks with conchoidal fracture); Specific gravity: 2.6–2.7
- Hardness
- 7 on Mohs scale
- Color
- Pink, white, or grey
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Pink, white, or grey; Luster: Vitreous to dull; Crystal structure: Non-foliated granoblastic; Cleavage: None (breaks with conchoidal fracture); Specific gravity: 2.6–2.7
Formation & geological history
Formed through the regional metamorphism of quartzose sandstone. Under high heat and pressure, the individual quartz grains recrystallize into a dense, interlocking mosaic of quartz crystals. Geological age varies by deposit, ranging from Precambrian to more recent tectonic events.
Uses & applications
Used as a decorative stone in landscaping, a crushed stone in road construction, as railroad ballast, and occasionally in glassmaking if high purity. It is also used as dimension stone for tiles and countertops.
Geological facts
Quartzite is so tough that it often survives intense weathering and erosion, forming the caps of many mountain ranges and ridges. Unlike sandstone, which breaks around grains, quartzite breaks through the grains.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by steel) and sandy, sugary texture on fresh surfaces. Commonly found in folded mountain belts. Collectors look for unique colorations caused by mineral impurities like hematite for pink hues.
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