metamorphic
Quartzite Cobble
Quartzite (chemically SiO2)
Hardness: 7 on Mohs scale; Color: Tan to off-white; Luster: Vitreous to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- Tan to off-white
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan to off-white; 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-rich sandstone under intense heat and pressure, often during mountain-building events. This specimen has been rounded by fluvial (water) erosion over long periods.
Uses & applications
Used in construction as crushed stone, road ballast, and decoratively in landscaping or as river rock. Large deposits are used for manufacturing glass and abrasives.
Geological facts
Quartzite is one of the most durable rocks on Earth, often forming the resistant 'cap' of mountains. It is harder than steel and can easily scratch a glass plate.
Field identification & locations
Identified by its extreme hardness, grainy 'sugar' texture on fresh surfaces, and lack of reaction to acid. Commonly found in riverbeds and glacial deposits.
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