metamorphic
Quartzite
Silicon Dioxide (SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, but iron staining creates yellow, orange, and tan hues; Luster: vitreous to waxy; Crystal structure: trigonal (hexagonal system), though appearing massive in this hand specimen; Cleavage: none, exhibits conchoidal or irregular fracture;…
- Hardness
- 7 on Mohs scale
- Luster
- vitreous to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray, but iron staining creates yellow, orange, and tan hues; Luster: vitreous to waxy; Crystal structure: trigonal (hexagonal system), though appearing massive in this hand specimen; Cleavage: none, exhibits conchoidal or irregular fracture; Specific gravity: approx 2.65.
Formation & geological history
Quartzite is a non-foliated metamorphic rock that forms when quartz-rich sandstone is subjected to high heat and pressure, causing the original quartz grains to recrystallize and fuse together. This specimen appears water-worn, likely from a fluvial (river) or glacial environment.
Uses & applications
Used widely in construction for railway ballast, decorative stone, and countertops. High-purity quartzite is also used to produce ferrosilicon, industrial silica sand, and silicon metal.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during weathering, forming the caps of ridges and mountains. It can be distinguished from its parent sandstone because it will break through its quartz grains rather than around them.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass and steel) and lack of reaction to acid. Often found in mountainous regions or as rounded cobbles in riverbeds. Look for a sugary or glassy texture on fresh breaks.
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