metamorphic
Quartzite Pebble
Quartzite (principally SiO2)
Hardness: 7 (Mohs scale); Color: White to light grey with iron staining (tan/orange); Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 (Mohs scale)
- Color
- White to light grey with iron staining (tan/orange)
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: White to light grey with iron staining (tan/orange); Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Quartzite is formed when quartz-rich sandstone is subjected to high heat and pressure during regional metamorphism, causing the quartz grains to recrystallize and fuse into a dense rock. This specimen has been further shaped into a rounded pebble by water erosion.
Uses & applications
Used in construction as road ballast, in the glass industry as a source of silica, and as decorative stone in landscaping or as pocket stones for collectors.
Geological facts
Quartzite is so tough that it often survives intense erosion that wears away surrounding softer rocks. It can be distinguished from sandstone because it breaks through the quartz grains rather than around them.
Field identification & locations
Identify in the field by its extreme hardness (it will scratch glass) and lack of reaction to acid. Commonly found in riverbeds, glacial deposits, and mountain ranges.
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