metamorphic
Quartzite Cobble
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: tan, grey, cream with iron staining; Luster: dull to vitreous; Structure: granoblastic, non-foliated; Cleavage: none; extremely durable.
- Hardness
- 7 on Mohs scale
- Color
- tan, grey, cream with iron staining
- Luster
- dull to vitreous
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Physical properties
Hardness: 7 on Mohs scale; Color: tan, grey, cream with iron staining; Luster: dull to vitreous; Structure: granoblastic, non-foliated; Cleavage: none; extremely durable.
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone. High heat and pressure originaly fused sand grains into a solid rock. This specific specimen was later rounded by water erosion in a river or glacial environment.
Uses & applications
Commonly used as crushed stone in construction, road ballast, or as decorative garden landscape rocks. Due to its hardness, it is historically used for primitive tools.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the caps of mountains and ridges. It is one of the most durable rocks found in nature, often outlasting the rocks around it.
Field identification & locations
Identify in the field by its inability to be scratched by a steel blade and its lack of reaction to acid. Often found in riverbeds, moraines, and beaches as smooth, rounded 'cobbles'.
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