metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, often with yellow or reddish iron staining; Luster: vitreous (glassy) to dull; Crystal structure: trigonal (microcrystalline); Fracture: conchoidal; Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Luster
- vitreous (glassy) to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray, often with yellow or reddish iron staining; Luster: vitreous (glassy) to dull; Crystal structure: trigonal (microcrystalline); Fracture: conchoidal; Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the regional metamorphism of quartz sandstone. Subjected to high heat and pressure, causing the original quartz sand grains to recrystallize and fuse together. Can range from Precambrian to any age of buried sandstone.
Uses & applications
Used in construction as crushed stone for road bases and railroad ballast. High-purity quartzite is used to produce silica sand for glassmaking and industrial abrasives. Used as an architectural dimension stone and for countertops.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during erosion, often forming the caps of ridges and mountains. It is harder than steel and will easily scratch a knife blade.
Field identification & locations
Identify in the field by its hardness (it should scratch glass) and its sugary texture. Unlike sandstone, quartzite breaks through its grains rather than around them. Found globally in mountainous regions or ancient Canadian/African shields.
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