metamorphic
Quartzite (likely iron-stained)
Quartzite; predominantly recrystallized SiO₂ (quartz), with iron-oxide staining
AI-generated identification · may be incorrectTypically very hard (Mohs 7), tan to rusty brown, granular and sugary, with a vitreous to dull luster; quartz grains are tightly interlocked and cleavage is absent. The pictured fragment appears dense and angular, though identification is limited by the image.
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Physical properties
Typically very hard (Mohs 7), tan to rusty brown, granular and sugary, with a vitreous to dull luster; quartz grains are tightly interlocked and cleavage is absent. The pictured fragment appears dense and angular, though identification is limited by the image.
Formation & geological history
Forms when quartz-rich sandstone is subjected to heat and pressure, commonly during regional metamorphism; its age depends on the source sandstone and metamorphic event. Iron oxides produce the tan-orange coloration.
Uses & applications
Used as crushed stone, aggregate, paving, countertops, and dimension stone; attractive pieces are collected or used decoratively, but this fragment has little gem value.
Geological facts
Quartzite commonly resists weathering more strongly than surrounding rocks and can form prominent ridges. Unlike marble, it does not fizz with dilute hydrochloric acid unless contaminated by carbonate minerals.
Field identification & locations
Look for interlocking quartz grains, extreme hardness, and inability to scratch with a steel knife; a streak test is usually white. Common occurrences include metamorphic mountain belts worldwide, including the Appalachians, Rocky Mountains, Alps, and India.
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