metamorphic
Quartzite Pebble
Metamorphic Quartzite (SiO2)
Hardness: 7 (Mohs scale), Color: light grey/greenish, Luster: Vitreous to dull, Crystal structure: Hexagonal/trigonal granular, Cleavage: None (fractures conchoidally), Specific gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: light grey/greenish, Luster: Vitreous to dull, Crystal structure: Hexagonal/trigonal granular, Cleavage: None (fractures conchoidally), Specific gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under high heat and pressure, typically during mountain-building events. This specimen has been rounded into a pebble by water erosion.
Uses & applications
Common quartzite is used in construction as crushed stone or ballast. Rounded pebbles are popular for landscaping, aquarium decor, and aggregate in concrete.
Geological facts
Quartzite is so durable that it often remains as caps on mountain peaks after softer rocks erode away. It is significantly harder than sandstone, making it difficult to quarry.
Field identification & locations
Identify in the field by its hardness (it will easily scratch glass) and lack of visible grains compared to sandstone. Commonly found in riverbeds or coastal deposits where metamorphic basement rock has eroded.
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