metamorphic
Quartzite
Metamorphosed sandstone (primarily SiO2)
Hardness: 7 on Mohs scale; Color: white, gray, or tan; Luster: vitreous to dull; Crystal structure: interlocking mosaic of quartz crystals; Cleavage: none; Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- white, gray, or tan
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: white, gray, or tan; Luster: vitreous to dull; Crystal structure: interlocking mosaic of quartz crystals; Cleavage: none; Specific gravity: 2.6-2.7
Formation & geological history
Formed when quartz-rich sandstone is subjected to high heat and pressure during regional metamorphism, typically at convergent plate boundaries. The sand grains recrystallize into a dense, interlocking stone.
Uses & applications
Used in construction as crushed stone for road beds or railroad ballast, as architectural dimensional stone for countertops and flooring, and in the manufacturing of glass and ceramics when high purity.
Geological facts
Quartzite is so hard and durable that it often forms the resistive caps of ridge-lines and mountains, withstanding weathering much better than surrounding softer rocks like shale or limestone.
Field identification & locations
Identify by its extreme hardness (it will scratch glass) and its sugary, crystalline texture. Unlike sandstone, quartzite breaks through the quartz grains rather than around them. Found globally in ancient mountain belts.
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