metamorphic
Quartzite
Metamorphic Quartzite (primarily SiO2)
Hardness: 7 (Mohs scale); Color: Yellow-brown, tan, and gray due to impurities; Luster: Vitreous to dull; Crystal structure: Non-foliated, granular; Cleavage: None; Specific gravity: 2.6–2.7
- Hardness
- 7 (Mohs scale)
- Color
- Yellow-brown, tan, and gray due to impurities
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Yellow-brown, tan, and gray due to impurities; Luster: Vitreous to dull; Crystal structure: Non-foliated, granular; Cleavage: None; Specific gravity: 2.6–2.7
Formation & geological history
Formed through the metamorphism of quartz sandstone under high heat and pressure, typically during mountain-building events (orogeny). The individual quartz grains recrystallize into an interlocking mosaic.
Uses & applications
Used in construction as crushed stone for road ballast, as a dimension stone for floor tiles and wall coverings, and occasionally in glassmaking if it is very pure.
Geological facts
Quartzite is so hard that it can scratch steel and glass easily. It is often more resistant to weathering than the surrounding rock, leading it to form prominent ridges or hilltops.
Field identification & locations
Identify in the field by its sugary, granular texture and extreme hardness. Unlike many other rocks, when hit with a hammer, it will break through the quartz grains rather than around them. Commonly found in folded mountain belts globally.
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