metamorphic
Quartz-rich metamorphic rock, likely quartzite
Quartzite; predominantly quartz (SiO₂), with minor iron-oxide and mica impurities
AI-generated identification · may be incorrectHardness about 7 Mohs; gray to tan, granular and irregularly crystalline, with a vitreous to dull luster. Quartzite lacks prominent cleavage and typically breaks across tightly interlocked quartz grains; the rusty colors suggest iron-oxide staining.
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Physical properties
Hardness about 7 Mohs; gray to tan, granular and irregularly crystalline, with a vitreous to dull luster. Quartzite lacks prominent cleavage and typically breaks across tightly interlocked quartz grains; the rusty colors suggest iron-oxide staining.
Formation & geological history
Forms when quartz-rich sandstone is buried and recrystallized under heat and pressure, commonly during mountain building. Its exact geological age cannot be determined from the photograph and depends on the source formation.
Uses & applications
Used as crushed stone, aggregate, road material, building stone, and occasionally countertops or decorative specimens. This small, unpolished piece has little gem or commercial value.
Geological facts
Quartzite is generally harder and more resistant than its sandstone precursor. A useful distinction is that quartz grains in true quartzite are fused into the rock rather than simply loosely cemented.
Field identification & locations
Common in metamorphic mountain belts worldwide, including the Appalachian Mountains, Rocky Mountains, and Precambrian shields. Scratch testing with a steel file is inconclusive; quartzite should resist it, while an unglazed ceramic streak test and inspection of fused grains help distinguish it from sandstone.
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