metamorphic
Quartzite
Quartzite (composed primarily of SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, but iron staining often creates yellow, orange, and reddish-brown hues; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None/Conchoidal fracture; Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray, but iron staining often creates yellow, orange, and reddish-brown hues; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None/Conchoidal fracture; Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. High heat and pressure cause the sand grains to recrystallize and fuse together, creating an extremely durable rock.
Uses & applications
Used in construction for road ballast, flooring, and decorative wall coverings. Because of its hardness, it is also used as a raw material in the manufacturing of glass and ceramics. Heartier specimens are popular as landscaping stones.
Geological facts
Quartzite is so hard that when broken, it fractures through the quartz grains rather than along the boundaries between them, which is a key distinction from sandstone. Some pure quartzite is more than 99% silica.
Field identification & locations
Identify by its inability to be scratched by a steel pocket knife and its grainy, crystalline texture. It is commonly found in mountainous regions or as river-tumbled 'cobbles'. Look for a sparkly, sugary appearance on fresh surfaces.
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