metamorphic
Quartz-rich quartzite or silicified stone
Quartzite; predominantly microcrystalline quartz (SiO₂), with minor iron-oxide staining and possible feldspar/clay impurities
AI-generated identification · may be incorrectHardness about 7 Mohs; off-white to tan with rusty brown patches, massive granular texture, and vitreous to dull luster. It lacks obvious cleavage and breaks irregularly or conchoidally; approximate specific gravity 2.6–2.7.
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Physical properties
Hardness about 7 Mohs; off-white to tan with rusty brown patches, massive granular texture, and vitreous to dull luster. It lacks obvious cleavage and breaks irregularly or conchoidally; approximate specific gravity 2.6–2.7.
Formation & geological history
Likely formed when quartz-rich sandstone was metamorphosed and recrystallized under heat and pressure, commonly during mountain-building; its exact geological age cannot be determined from the image. Alternatively, it may be a strongly silicified sedimentary cobble.
Uses & applications
Useful as durable aggregate, roadstone, building stone, landscaping material, and occasionally as a decorative polished stone; generally low jewelry value unless unusually patterned or gem-quality.
Geological facts
Quartzite is typically harder and more resistant to weathering than its sandstone parent, so it commonly survives as rounded stream or glacial cobbles. The tan and reddish colors usually result from iron oxides such as hematite or limonite.
Field identification & locations
Identify it by its very hard, quartz-rich surface: it should scratch glass and resist a steel knife, with no fizz in dilute hydrochloric acid. Common in metamorphic mountain belts and gravel deposits worldwide.
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