metamorphic
Quartzite Cobble
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: White to grayish with reddish iron-oxide staining; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- White to grayish with reddish iron-oxide staining
- Luster
- Vitreous to dull
Identified More metamorphic →
Explore Quartzite Cobble in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 7 on Mohs scale; Color: White to grayish with reddish iron-oxide staining; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. Under intense heat and pressure, quartz grains recrystallize and fuse together. This specimen appears water-worn, likely from a fluvial or glacial environment.
Uses & applications
Used as a decorative landscape stone, in construction as crushed stone for road ballast, or as a source of silica in glass manufacturing. Rounded cobbles are also used in Zen gardens.
Geological facts
Quartzite is so tough that it often survives geological cycles that destroy other rocks; it is harder and more durable than the sandstone from which it originated. It will scratch steel and glass.
Field identification & locations
Identify by its extreme hardness and sugary, crystalline texture where broken. Found globally in mountainous regions or as transported river/beach cobbles. This specific specimen shows iron staining from weathering.
