metamorphic
Quartzite
Quartzite (mostly SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan; Luster: vitreous to dull; Crystal structure: Non-foliated, interlocking quartz grains; Cleavage: none (breaks with conchoidal or irregular fracture).
- Hardness
- 7 on Mohs scale
- Color
- typically white, gray, or tan
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan; Luster: vitreous to dull; Crystal structure: Non-foliated, interlocking quartz grains; Cleavage: none (breaks with conchoidal or irregular fracture).
Formation & geological history
Quartzite forms from the metamorphism of quartz-rich sandstone. Under intense heat and pressure from tectonic activity, the original quartz sand grains recrystallize and fuse together into a dense, hard rock.
Uses & applications
Used extensively as crushed stone for road construction and railway ballast. Due to its hardness and resistance to weathering, high-quality specimens are used for countertops, flooring, and decorative stones in landscaping.
Geological facts
Quartzite is so hard that it can scratch steel and glass easily. In some mountain ranges, it forms resistant ridges because it withstands erosion better than surrounding softer rocks like limestone or shale.
Field identification & locations
Identify in the field by its hardness (cannot be scratched by a steel nail) and its grainy, sugary appearance despite being very dense. It is commonly found in folded mountain belts and ancient cratons worldwide.
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