metamorphic
Quartzite
Metamorphosed Quartz Sandstone (SiO2)
Hardness: 7 on Mohs scale; Color: White to light grey with tan staining; Luster: Vitreous to dull; Crystal structure: Non-foliated, granular; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- White to light grey with tan staining
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: White to light grey with tan staining; Luster: Vitreous to dull; Crystal structure: Non-foliated, granular; 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, typically during mountain-building events. The original quartz sand grains recrystallize into an interlocking mosaic.
Uses & applications
Used in construction as crushed stone or decorative aggregates, in the manufacture of glass and ceramics, and as a durable architectural stone for countertops and flooring.
Geological facts
Quartzite is so hard that it will scratch glass and even steel. It is often more resistant than the surrounding rocks, which is why it frequently forms the peaks of hills and mountain ranges.
Field identification & locations
Identify in the field by its hardness (will scratch glass) and its tendency to break through the sand grains rather than around them. Common in folded mountain belts like the Appalachians.
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