sedimentary
Sandstone (Weathered Cobble)
Clastic Sedimentary Rock (primarily SiO2)
Hardness: 6-7 (Mohs); Color: Tan, brown, or brownish-grey; Luster: Dull/Earthy; Crystal Structure: Clastic (grainy); Cleavage: None; Specific Gravity: 2.2-2.8.
- Hardness
- 6-7 (Mohs)
- Color
- Tan, brown, or brownish-grey
- Luster
- Dull/Earthy
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Physical properties
Hardness: 6-7 (Mohs); Color: Tan, brown, or brownish-grey; Luster: Dull/Earthy; Crystal Structure: Clastic (grainy); Cleavage: None; Specific Gravity: 2.2-2.8.
Formation & geological history
Formed through the accumulation and cementation of mineral particles or rock fragments (sand) over millions of years. This specific specimen shows 'rounding' due to fluvial (river) or glacial erosion, likely dating from the Paleozoic to Cenozoic eras depending on local geography.
Uses & applications
Used widely in construction as a building stone or aggregate. High-purity quartz sandstone is used in glass manufacturing. Smooth cobbles like this are often used in decorative landscaping.
Geological facts
Sandstone makes up about 20% of all sedimentary rocks on Earth. This specimen's teardrop shape suggests it was rolled in a high-energy water environment, such as a riverbed or shoreline, which smoothed its edges over time.
Field identification & locations
Identify by its 'sandpaper' feel and visible grains. Common in riverbeds, deserts, and coastal areas globally. For collectors, look for cross-bedding or fossil inclusions which increase interest.
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