metamorphic
Quartzite Cobble
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: light gray to tan with mottled spots; Luster: dull to vitreous; Crystal structure: Non-foliated granoblastic; Cleavage: None; Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- light gray to tan with mottled spots
- Luster
- dull to vitreous
Identified More metamorphic →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 7 on Mohs scale; Color: light gray to tan with mottled spots; Luster: dull to vitreous; Crystal structure: Non-foliated granoblastic; Cleavage: None; Specific gravity: 2.6-2.7
Formation & geological history
Formed from the metamorphism of quartz sandstone under high heat and pressure, often during mountain-building events (Orogeny). This specific specimen has been rounded into a cobble shape by water erosion.
Uses & applications
Commonly used in construction as crushed stone for roadbeds, as decorative landscape stones, and occasionally as a source of silica for glassmaking.
Geological facts
Quartzite is so durable that it often survives multiple cycles of erosion and redeposition. It is harder than steel and can easily scratch glass.
Field identification & locations
Identify in the field by its extreme hardness and grainy sand-like texture that does not rub off. Found in riverbeds, glacial tills, and ancient mountain ranges.
More like this
