metamorphic
Quartzite
Metamorphic Quartzite (SiO2)
Hardness of 7 on the Mohs scale; color ranges from white and gray to pink, yellow, or brown due to iron oxide impurities; vitreous to greasy luster; non-foliated crystal structure with interlocking quartz crystals; no true cleavage; specific gravity around 2.65.
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Physical properties
Hardness of 7 on the Mohs scale; color ranges from white and gray to pink, yellow, or brown due to iron oxide impurities; vitreous to greasy luster; non-foliated crystal structure with interlocking quartz crystals; no true cleavage; specific gravity around 2.65.
Formation & geological history
Formed from quartz-rich sandstone or chert under high temperature and pressure associated with tectonic compression during regional metamorphism, often over millions of years.
Uses & applications
Used in construction, as crushed stone for roadbeds, railway ballast, manufacturing of silica brick, and sometimes as a decorative dimension stone or in countertops.
Geological facts
Quartzite is extremely durable and resistant to chemical weathering, which is why ridges formed of quartzite often survive as prominent hills or mountains after softer surrounding rocks have eroded away.
Field identification & locations
Identified in the field by its hardness (it will easily scratch glass and cannot be scratched by a knife) and the sugary texture of interlocking quartz grains on freshly broken surfaces. Found worldwide in mountainous regions and ancient orogenic belts.
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