metamorphic
Quartzite
Quartzite (composed primarily of SiO2)
Hardness: 7 on Mohs scale; Color: white, grey, beige with slight pinkish hues; Luster: vitreous to grainy; Crystal structure: Non-foliated, granular; Cleavage: none (fractures conchoidally); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- white, grey, beige with slight pinkish hues
- Luster
- vitreous to grainy
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Physical properties
Hardness: 7 on Mohs scale; Color: white, grey, beige with slight pinkish hues; Luster: vitreous to grainy; Crystal structure: Non-foliated, granular; Cleavage: none (fractures conchoidally); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz sandstone under high heat and pressure, causing the original quartz grains to recrystallize into an interlocking mosaic. Its geological age can range from Precambrian to Cenozoic depending on the source region.
Uses & applications
Used extensively in construction as road ballast, roofing tiles, and decorative stone. High-purity quartzite is used to produce ferrosilicon, industrial silica sand, and silicon metal.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rock, forming resistant ridges and hilltops. Unlike sandstone, which breaks around grains, quartzite breaks through the grains due to its densely recrystallized nature.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass) and its sugary, granular texture. It is commonly found in mountain ranges and glacial deposits. Collectors value it for tumbling or as yard specimens.
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