metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale. Color: Light gray, white, or yellowish. Luster: Vitreous to dull. Crystal structure: Trigonal (microcrystalline). Cleavage: None (conchoidal fracture). Specific Gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- Light gray, white, or yellowish
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale. Color: Light gray, white, or yellowish. Luster: Vitreous to dull. Crystal structure: Trigonal (microcrystalline). Cleavage: None (conchoidal fracture). Specific Gravity: 2.6-2.7.
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone through heat and pressure, typically during mountain-building events (orogeny). Often found in Precambrian and Paleozoic rock formations.
Uses & applications
Used in construction as road ballast, decorative stone, and dimension stone for flooring or countertops. High-purity quartzite is used to produce silica sand for glassmaking.
Geological facts
Quartzite is so tough that it usually breaks through the quartz grains rather than along their boundaries, unlike the sandstone from which it originated. It is one of the most chemically resistant and physically durable rocks on Earth's surface.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass) and its grainy, sugary texture. It is commonly found in folded mountain ranges and as rounded cobbles in riverbeds. Look for a lack of effervescence when tested with acid.
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