metamorphic
Quartzite Cobble
Quartzite (mostly SiO2)
Hardness: 7 on Mohs scale; Color: light grey to white; Luster: vitreous or dull; Structure: Granular/Crystalline; Specific Gravity: 2.6-2.7. Extremely durable and resistant to scratching.
- Hardness
- 7 on Mohs scale
- Color
- light grey to white
- Luster
- vitreous or dull
Identified More metamorphic →
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Physical properties
Hardness: 7 on Mohs scale; Color: light grey to white; Luster: vitreous or dull; Structure: Granular/Crystalline; Specific Gravity: 2.6-2.7. Extremely durable and resistant to scratching.
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone under intense heat and pressure. This specific specimen has been rounded into a cobble by water erosion (clastic transport).
Uses & applications
Used in construction as road ballast, railway ballast, and decorative garden stone. High-purity quartzite is used to produce glass and metallic silicon.
Geological facts
Quartzite is so tough that it often breaks through the individual quartz grains rather than around them, unlike sandstone. It is one of the most physically durable rocks on Earth's surface.
Field identification & locations
Identify by its ability to scratch glass and its grainy, sandpaper-like surface that doesn't rub off. Commonly found in riverbeds and glacial deposits.
