metamorphic
Quartzite
Metamorphic Quartzite (SiO2)
Hardness of 7 on the Mohs scale, colors ranging from white and gray to pink, yellow, or brown due to iron oxide impurities. Vitreous to dull luster depending on weathering, massive to granular crystal structure with interlocking quartz crystals, lacking distinct cleavage.
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Physical properties
Hardness of 7 on the Mohs scale, colors ranging from white and gray to pink, yellow, or brown due to iron oxide impurities. Vitreous to dull luster depending on weathering, massive to granular crystal structure with interlocking quartz crystals, lacking distinct cleavage.
Formation & geological history
Formed when quartz-rich sandstone or chert is subjected to high heat and pressure, typically during tectonic mountain-building events (regional metamorphism). Geological age can range from Precambrian to Cenozoic.
Uses & applications
Used heavily in construction as crushed stone for road bases, railway ballast, dimension stone, manufacturing silica brick, and sometimes as a decorative landscape or sculptural stone.
Geological facts
Because quartzite is extremely resistant to weathering and chemical breakdown, it often forms prominent ridges, hills, and resistant capping layers in mountain ranges long after surrounding softer rocks have eroded away.
Field identification & locations
Can be identified in the field by its extreme hardness (scratches glass easily, cannot be scratched by a knife), lack of reaction to acid, and the fact that it fractures through quartz grains rather than around them. Found globally where ancient sandstones underwent metamorphism.
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