metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan but can be reddish; Luster: vitreous to dull; Crystal structure: Non-foliated, interlocking quartz grains; Cleavage: none (conchoidal fracture).
- Hardness
- 7 on Mohs scale
- Color
- typically white, gray, or tan but can be reddish
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan but can be reddish; Luster: vitreous to dull; Crystal structure: Non-foliated, interlocking quartz grains; Cleavage: none (conchoidal fracture).
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure reciprocal to tectonic activity cause the sand grains to recrystallize and fuse together. These are globally ancient rocks often associated with mountain ranges.
Uses & applications
Used as crushed stone for road construction and railway ballast. Due to its hardness, it is also used for floor tiles, countertops, and decorative carvings.
Geological facts
Quartzite is so hard that when it breaks, it fractures through the quartz grains rather than along the boundaries between them, unlike its parent rock, sandstone.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass and steel) and its crystalline, sugary appearance. It is commonly found in beach or river cobbles and used as a durable building material.
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