metamorphic
Quartzite Cobble
Quartzite (SiO2 based metamorphic rock)
Hardness: 7 on Mohs scale; Color: Grayish-white to light tan; Luster: Dull (weathered) to vitreous (fresh break); Texture: Fine-grained and non-foliated; Cleavage: None (conchoidal fracture)
- Hardness
- 7 on Mohs scale
- Color
- Grayish-white to light tan
- Luster
- Dull (weathered) to vitreous (fresh break)
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Physical properties
Hardness: 7 on Mohs scale; Color: Grayish-white to light tan; Luster: Dull (weathered) to vitreous (fresh break); Texture: Fine-grained and non-foliated; Cleavage: None (conchoidal fracture)
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone under intense heat and pressure. This specimen shows significant rounding, suggesting it was transport by water (river or glacial) over a long period.
Uses & applications
Commonly used in construction as crushed stone or road ballast, as a decorative garden stone, and historically for stone tools due to its hardness and durability.
Geological facts
Quartzite is one of the most physically durable and chemically resistant rocks found on Earth's surface. It is often harder than the steel blade of a pocket knife.
Field identification & locations
Identified in the field by its extreme hardness (cannot be scratched by steel) and lack of reaction to acid. Often found in riverbeds, glacial tills, and mountainous regions like the Appalachians or the Alps.
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