metamorphic
Quartzite
Quartzite (composed primarily of SiO2)
Hardness: 7 (Mohs scale); Color: light grey to tan with iron staining; Luster: vitreous to grainy; Crystal structure: trigonal (recrystallized); Cleavage: none; Specific gravity: 2.6-2.65
- Hardness
- 7 (Mohs scale)
- Color
- light grey to tan with iron staining
- Luster
- vitreous to grainy
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Physical properties
Hardness: 7 (Mohs scale); Color: light grey to tan with iron staining; Luster: vitreous to grainy; Crystal structure: trigonal (recrystallized); Cleavage: none; Specific gravity: 2.6-2.65
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure, typically during mountain-building events. This specimen appears water-worn from a river or coastal environment.
Uses & applications
Used extensively in road construction, railway ballast, and as a decorative stone in landscaping. High-purity quartzite is used to produce silica sand for glassmaking and industrial abrasives.
Geological facts
Quartzite is so hard and durable that it often forms the ridges and peaks of mountain ranges because it resists erosion better than the surrounding rocks. It is harder than a steel knife and will scratch glass easily.
Field identification & locations
Identified in the field by its sugary, crystalline texture and extreme hardness. Unlike limestone, it will not fizz with acid. Commonly found in metamorphic belts and as rounded cobbles in high-energy stream beds.
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