metamorphic
Quartzite Cobble
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: Pinkish-tan with white mottling; Luster: Non-foliated, vitreous to dull; Crystal Structure: Granular/Massive; Cleavage: None (conchoidal fracture).
- Hardness
- 7 on Mohs scale
- Color
- Pinkish-tan with white mottling
- Luster
- Non-foliated, vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Pinkish-tan with white mottling; Luster: Non-foliated, vitreous to dull; Crystal Structure: Granular/Massive; Cleavage: None (conchoidal fracture).
Formation & geological history
Formed from the metamorphism of quartz sandstone under intense heat and pressure, typically during mountain-building events. These water-worn cobbles are often found in riverbeds or glacial tills.
Uses & applications
Used primarily in construction as crushed stone or road ballast, as decorative landscaping gravel, and as a source of silica for industrial processes.
Geological facts
Quartzite is so durable that it often survives multiple cycles of erosion and deposition, outlasting the softer rocks that once surrounded it. Its pink hue is usually caused by trace amounts of iron oxide.
Field identification & locations
Identified in the field by its extreme hardness (cannot be scratched by a steel knife) and lack of reaction to acid. Often found in areas with past glacial activity or high-energy stream beds.
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