metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: Yellow, tan, or brown (due to iron oxide staining); Luster: Vitreous to dull; Crystal Structure: Granular/Massive; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Yellow, tan, or brown (due to iron oxide staining)
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Yellow, tan, or brown (due to iron oxide staining); Luster: Vitreous to dull; Crystal Structure: Granular/Massive; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed from the metamorphism of quartz sandstone under intense heat and pressure. The original quartz grains recrystallize and fuse together into a dense, interlocking mosaic of crystals. Age can range from Precambrian to Cenozoic.
Uses & applications
Used as a decorative stone in architecture, as crushed stone for road construction, as railroad ballast, and occasionally in glassmaking if pure enough. High-quality varieties are used for kitchen countertops and lapidary work.
Geological facts
Quartzite is so tough that it usually breaks across the quartz grains rather than around them, unlike its parent rock sandstone. It is highly resistant to chemical weathering and creates prominent ridges in many mountain ranges.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by steel) and lack of reaction to acid. It often appears sugary or grainy but feels smooth to the touch. Commonly found in folded mountain belts globally.
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