metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 (Mohs scale), Color: White, gray, or tan with banding, Luster: Vitreous to dull, Crystal Structure: Hexagonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7.
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Physical properties
Hardness: 7 (Mohs scale), Color: White, gray, or tan with banding, Luster: Vitreous to dull, Crystal Structure: Hexagonal (microcrystalline), 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 in orogenic belts. This specimen shows a water-worn, rounded shape suggesting fluvial or coastal erosion.
Uses & applications
Used in construction as crushed stone, road ballast, or decorative landscaping stones. Highly pure quartzite is used to produce silica sand 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 can be distinguished by its ability to scratch glass.
Field identification & locations
Identify in the field by its hardness (cannot be scratched by a steel nail) and grainy, sugary texture under a lens. Commonly found in ancient mountain ranges and glacial till.
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