metamorphic
Quartzite
Metamorphosed Quartz Sandstone
Hardness: 7 (Mohs scale); Color: Tan, brown, and yellow; Luster: Dull to vitreous; Structure: Neocrystalline/Granular; Cleavage: None; Specific Gravity: 2.6-2.7
- Hardness
- 7 (Mohs scale)
- Color
- Tan, brown, and yellow
- Luster
- Dull to vitreous
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Physical properties
Hardness: 7 (Mohs scale); Color: Tan, brown, and yellow; Luster: Dull to vitreous; Structure: Neocrystalline/Granular; Cleavage: None; Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure, typically in convergent plate boundaries. The original sand grains recrystallize into a locked mosaic of quartz crystals.
Uses & applications
Used primarily in construction as crushed stone for road ballast, floor tiles, roofing granules, and as a decorative stone in landscaping. High-purity quartzite is used to produce silica for glassmaking.
Geological facts
Quartzite is so tough that it often survives intense weathering better than the surrounding rocks, which creates high ridges and resistant mountains. It is harder than steel and can easily scratch a glass plate.
Field identification & locations
Identify in the field by its grainy, 'sugary' texture and the way it breaks through the quartz grains rather than around them (unlike sandstone). Commonly found in ancient mountain belts and riverbeds as rounded cobbles.
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