metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: Pinkish-tan to light gray; Luster: Dull to vitreous; Crystal structure: Trigonal (microcrystalline); Cleavage: None, fractures conchoidally; Specific gravity: 2.6 - 2.7.
- Hardness
- 7 on Mohs scale
- Color
- Pinkish-tan to light gray
- Luster
- Dull to vitreous
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Physical properties
Hardness: 7 on Mohs scale; Color: Pinkish-tan to light gray; Luster: Dull to vitreous; Crystal structure: Trigonal (microcrystalline); Cleavage: None, fractures conchoidally; Specific gravity: 2.6 - 2.7.
Formation & geological history
Formed from the metamorphism of quartz sandstone under intense heat and pressure, typically during mountain-building events. The individual quartz grains recrystallize into a dense, interlocking mosaic of quartz crystals.
Uses & applications
Used as a decorative stone in landscaping, crushed stone for road construction and railway ballast, and occasionally for high-end countertops or as a source of silica for glass manufacturing.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rock in weathering processes, resulting in prominent ridges or 'monadnocks' in the landscape. It is harder than steel and will scratch glass easily.
Field identification & locations
Identify by its extreme hardness and sugary, crystalline texture upon a fresh fracture. It is commonly found in ancient mountain belts and riverbeds as rounded cobbles due to its durability.
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