metamorphic
Quartzite Cobble
Quartzite (principally SiO2)
Hardness: 7 on Mohs scale; Color: tan, yellowish-brown with dark inclusions; Luster: dull to vitreous; Crystal Structure: Granular/Crystalline; Cleavage: None; SG: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- tan, yellowish-brown with dark inclusions
- Luster
- dull to vitreous
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Physical properties
Hardness: 7 on Mohs scale; Color: tan, yellowish-brown with dark inclusions; Luster: dull to vitreous; Crystal Structure: Granular/Crystalline; Cleavage: None; SG: 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 and smoothed by water transport in a river or coastal environment.
Uses & applications
Used as a construction aggregate, for road base, decorative landscaping, and occasionally as a source for high-purity silica in glass making.
Geological facts
Quartzite is so hard that it can scratch glass and steel. It is one of the most durable rocks on Earth, which is why cobbles like this survive millions of years of erosion.
Field identification & locations
Identify by its hardness (will scratch a knife blade) and granular texture that looks like sugar. Common in river beds and glacial deposits worldwide. Highly resistant to chemical weathering.
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