sedimentary
Sandstone (Water-worn Cobble)
Arenite (SiO2 with CaCO3 or Fe2O3 cement)
Hardness: 6-7 Mohs; Color: Tan, beige, or light brown; Luster: Dull/Earthy; Structure: Clastic, granular texture; Specific Gravity: 2.2-2.8; Notable for its pitted, weathered surface and rounded edges from fluvial erosion.
- Hardness
- 6-7 Mohs
- Color
- Tan, beige, or light brown
- Luster
- Dull/Earthy
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Physical properties
Hardness: 6-7 Mohs; Color: Tan, beige, or light brown; Luster: Dull/Earthy; Structure: Clastic, granular texture; Specific Gravity: 2.2-2.8; Notable for its pitted, weathered surface and rounded edges from fluvial erosion.
Formation & geological history
Formed from the accumulation and lithification of sand-sized mineral grains or rock fragments. This specific specimen has undergone significant physical weathering and water-based erosion in a river or coastal environment, creating its smooth, rounded 'cobble' shape.
Uses & applications
Commonly used in construction as building stone, road base, and decorative landscaping. In industry, high-purity sandstone is used as a source of silica for glass manufacturing.
Geological facts
The unique 'face-like' appearance of this rock is an example of pareidolia, where natural weathering or differential erosion creates shapes that humans perceive as familiar objects. Many famous natural landmarks, like the 'Old Man of the Mountain', are formed this way.
Field identification & locations
Identify in the field by its gritty texture (feels like sandpaper) and visible sand grains. Found globally in basins, riverbeds, and sedimentary outcrops. For collectors, examples with unusual shapes (like this one) are often kept as conversation pieces or 'garden art'.
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