metamorphic
Quartzite
Quartzite (principally SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, but often yellow, tan, or red due to impurities; Luster: vitreous to grainy; Crystal structure: Trigonal (microcrystalline); Cleavage: none, breaks with a conchoidal or irregular fracture.
- 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, but often yellow, tan, or red due to impurities; Luster: vitreous to grainy; Crystal structure: Trigonal (microcrystalline); Cleavage: none, breaks with a conchoidal or irregular fracture.
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone under intense heat and pressure. This process causes the original quartz grains to recrystallize and fuse together into a dense, hard rock.
Uses & applications
Used in construction as a decorative stone, road ballast, sand for glassmaking, and frequently used for high-end kitchen countertops due to its durability.
Geological facts
Quartzite is so hard that it will scratch glass and even steel. In many areas, quartzite ridges remain standing as high mountains long after softer rocks have eroded away around them.
Field identification & locations
Identify in the field by its extreme hardness and its sugary, crystalline appearance on a fresh break. It lacks the well-defined layers of the parent sandstone and will not fizz when in contact with acid, unlike marble.
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