metamorphic
Quartzite
Metamorphosed Quartz Sandstone (SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray; Luster: vitreous (glassy) to dull; Crystal structure: Trigonal (microcrystalline); Fracture: conchoidal or uneven grains; Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- typically white to gray
- Luster
- vitreous (glassy) to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray; Luster: vitreous (glassy) to dull; Crystal structure: Trigonal (microcrystalline); Fracture: conchoidal or uneven grains; Specific gravity: 2.6-2.7.
Formation & geological history
Formed when quartz-rich sandstone is subjected to high heat and pressure during regional metamorphism. This process causes the original quartz grains to recrystallize and fuse together into a dense, interlocking network.
Uses & applications
Used extensively in construction as crushed stone for road beds and railway ballast. Due to its durability and resistance to weathering, it is used for floor tiles, stairs, and countertops. High-purity quartzite is used to produce silica sand for glassmaking.
Geological facts
Quartzite is so tough that it often survives intense weathering that wears away softer rocks, frequently forming the peaks of mountain ranges. It is one of the hardest and most chemically resistant rocks found on the Earth's surface.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass) and its sugary, crystalline appearance on a fresh break. Unlike sandstone, which breaks around the grains, quartzite breaks across the grains. It is ubiquitous in mountainous regions worldwide.
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