metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale. Color: Light gray to white with occasional yellowish or greenish highlights. Luster: Vitreous to dull when weathered. Structure: Granoblastic, non-foliated. Cleavage: None (breaks with conchoidal fracture). Specific Gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Luster
- Vitreous to dull when weathered
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Physical properties
Hardness: 7 on Mohs scale. Color: Light gray to white with occasional yellowish or greenish highlights. Luster: Vitreous to dull when weathered. Structure: Granoblastic, non-foliated. Cleavage: None (breaks with conchoidal fracture). Specific Gravity: 2.6-2.7.
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. Under intense heat and pressure, quartz grains recrystallize and fuse together, creating a dense, interlocking matrix. This usually occurs during mountain-building events (orogenies).
Uses & applications
Commonly used as crushed stone in road construction and railway ballast. Due to its hardness and resistance to weathering, it is used for floor tiles, countertops, and as building stone decoration. High-purity quartzite is a source of silica for glassmaking.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rock, forming resistant ridges and hilltops. It is frequently mistaken for marble, but unlike marble, it will not fizz when exposed to acid and is much harder.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and its grainy, sandpaper-like texture that has been fused into a crystalline mass. It is found globally in ancient shield areas and folded mountain belts.
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