metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, often with yellow or brownish staining from iron; Luster: Vitreous to dull; Crystal structure: Non-foliated, interlocking quartz grains; Cleavage: None (fractures across grains).
- Hardness
- 7 on Mohs scale
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray, often with yellow or brownish staining from iron; Luster: Vitreous to dull; Crystal structure: Non-foliated, interlocking quartz grains; Cleavage: None (fractures across grains).
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure cause the original quartz grains to recrystallize and fuse together. These rocks can date from various geological periods, often hundreds of millions of years old.
Uses & applications
Used as crushed stone for road construction and railway ballast; in its purer form, used for manufacturing glass, ceramics, and as a decorative stone in architecture and interior design.
Geological facts
Quartzite is so tough that when it breaks, it fractures through the quartz grains rather than along the boundaries between them, unlike its parent rock, sandstone. It is resistant to chemical weathering.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass) and lack of foliation or distinct layering compared to gneiss. This specimen is a 'river cobble,' smoothed and rounded by water transport in a stream or riverbed.
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