metamorphic
Quartzite (Tumbled Pebble)
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: Off-white to light gray with slight translucency; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None; Specific gravity: 2.63–2.65
- Hardness
- 7 on Mohs scale
- Color
- Off-white to light gray with slight translucency
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Off-white to light gray with slight translucency; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None; Specific gravity: 2.63–2.65
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure, causing quartz grains to recrystallize and fuse together. Often found in orogenic (mountain-building) belts.
Uses & applications
Used as crushed stone for road construction, railway ballast, and in the manufacturing of glass and ceramics. Polished pebbles are common in landscaping and home decor.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rock during erosion, frequently forming the tops of ridges and mountains. It is harder than a steel knife and will easily scratch glass.
Field identification & locations
Identify in the field by its extreme hardness and grainy, sugary texture. Unlike marble, it will not fizz with acid. Common in riverbeds and glacial deposits as rounded pebbles like the one shown.
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