metamorphic
Weathered quartz-rich rock, likely quartzite or altered sandstone
Quartzite (mostly microcrystalline quartz, SiO₂); exact identification is uncertain from the photograph
AI-generated identification · may be incorrectTan to gray-brown, opaque, earthy to weakly vitreous luster, irregular granular texture, and no obvious cleavage; quartz hardness is about Mohs 7, with specific gravity near 2.65. Its rounded, weathered surface suggests abrasion or surface alteration.
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Physical properties
Tan to gray-brown, opaque, earthy to weakly vitreous luster, irregular granular texture, and no obvious cleavage; quartz hardness is about Mohs 7, with specific gravity near 2.65. Its rounded, weathered surface suggests abrasion or surface alteration.
Formation & geological history
Quartzite forms when quartz-rich sandstone is metamorphosed and recrystallized under heat and pressure, commonly during mountain-building; sandstone protoliths may be hundreds of millions to billions of years old. It may also be strongly silicified sandstone, which can look similar.
Uses & applications
Used as crushed aggregate, road stone, building stone, and decorative material; attractive pieces may be collected, but this specimen has no apparent gemstone-grade value.
Geological facts
Quartz-rich rocks commonly resist weathering, leaving rounded cobbles while softer minerals erode away. Iron-oxide staining likely produces the brown coloration.
Field identification & locations
Look for a gritty or sugary quartz texture, very high hardness, and inability to scratch quartz or glass; diluted acid should not fizz unless carbonate minerals are present. Common in metamorphic belts and quartz-rich stream gravels.
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