metamorphic
Tumbled quartzite pebble
Quartzite; predominantly microcrystalline quartz (SiO₂)
AI-generated identification · may be incorrectHardness about 7 Mohs; tan to pink-beige with subtle white veining, dull to weakly vitreous luster, very fine-grained interlocking quartz crystals, and no visible cleavage. The rounded shape indicates natural abrasion or tumbling.
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Physical properties
Hardness about 7 Mohs; tan to pink-beige with subtle white veining, dull to weakly vitreous luster, very fine-grained interlocking quartz crystals, and no visible cleavage. The rounded shape indicates natural abrasion or tumbling.
Formation & geological history
Quartzite forms when quartz-rich sandstone is metamorphosed under heat and pressure, commonly during mountain-building; its exact age cannot be determined from the photograph. It occurs in exposed metamorphic belts and as durable stream or beach pebbles derived from them.
Uses & applications
Used as crushed stone, aggregate, paving, and building or decorative stone; attractive polished pieces are sold as inexpensive lapidary specimens. Typical value is about $2–$15 for a small tumbled pebble, or $10–$40 for a larger polished specimen.
Geological facts
Quartzite is generally more resistant to weathering than its parent sandstone and can form prominent ridges and hills. Some varieties resemble jasper or marble but are substantially harder than calcite-rich marble.
Field identification & locations
Identify it by its sugary quartz texture, hardness, and inability to scratch with a steel knife; quartz grains commonly fracture across the rock rather than separating along bedding. Common sources include metamorphic mountain regions and gravel deposits worldwide.
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