metamorphic
Quartzite
Quartzite (composed primarily of SiO2)
Mohs hardness: 7, color: tan to light brown with sugary texture, luster: vitreous to dull, crystal structure: hexagonal, cleavage: none (conchoidal fracture), specific gravity: 2.6-2.7
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Physical properties
Mohs hardness: 7, color: tan to light brown with sugary texture, luster: vitreous to dull, crystal structure: hexagonal, cleavage: none (conchoidal fracture), specific gravity: 2.6-2.7
Formation & geological history
Formed from the metamorphism of quartz sandstone under high heat and pressure, causing the original quartz grains to recrystallize into a dense interlaced structure. Generally very old, typically Precambrian or Paleozoic.
Uses & applications
Used as a decorative stone in construction, road ballast, railway tracks, and sometimes as a source of silica for glass making.
Geological facts
Quartzite is so tough that it often forms the ridges and peaks of mountain ranges because it resists weathering far better than the surrounding rocks. When struck with a hammer, it typically breaks through the quartz grains rather than around them.
Field identification & locations
Identify in the field by its hardness (will scratch glass easily) and its distinct 'sugary' or granular appearance on a freshly broken surface. Found worldwide in mountain belts.
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