metamorphic
Quartzite Cobble
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, white, and yellowish with grey banding; Luster: Vitreous to dull (waxy when wet); Crystal Structure: Granular, non-foliated metamorphosed quartz grains; Cleavage: None (conchoidal fracture).
- Hardness
- 7 on Mohs scale
- Color
- Tan, white, and yellowish with grey banding
- Luster
- Vitreous to dull (waxy when wet)
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, white, and yellowish with grey banding; Luster: Vitreous to dull (waxy when wet); Crystal Structure: Granular, non-foliated metamorphosed quartz grains; 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 specific specimens are water-worn river or beach stones.
Uses & applications
Used as construction aggregate, decorative landscaping stone, and occasionally as a source of silica for industrial manufacturing.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during erosion, ending up as rounded cobbles in riverbeds. It is often harder than the steel of a pocket knife.
Field identification & locations
Identify in the field by its inability to be scratched by a steel blade and its granular, sugary appearance on a fresh break. Common in glacial till and riverbeds.
