metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, often with reddish or brown iron staining; Luster: vitreous to grainy; Crystal structure: Trigonal (granular texture); Cleavage: none, breaks with conchoidal or uneven fracture; Specific Gravity: 2.6 - 2.7
- Hardness
- 7 on Mohs scale
- Luster
- vitreous to grainy
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray, often with reddish or brown iron staining; Luster: vitreous to grainy; Crystal structure: Trigonal (granular texture); Cleavage: none, breaks with conchoidal or uneven fracture; Specific Gravity: 2.6 - 2.7
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. Under intense heat and pressure, the individual quartz grains recrystallize and fuse together into a dense, hard rock. This specimen appears to have weathered surface features common in fluvial or glacial deposits.
Uses & applications
Commonly used in construction as crushed stone for road beds, railroad ballast, and concrete aggregate. High-purity quartzite is used to produce silica sand for glassmaking and industrial abrasives. Smooth river-worn specimens are used in landscaping.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during erosion, frequently forming the peaks of mountain ranges. It is harder than steel and will easily scratch a knife blade or glass plate.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel nail) and its granular, sugary appearance on a fresh break. Unlike sandstone, quartzite breaks through the grains rather than around them. Found globally in mountainous metamorphic terrains.
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