Where is Weathered Sedimentary Rock found?
Sedimentary rock (likely sandstone or siltstone) with weathering rind
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Open the appWeathered Sedimentary Rock occurs in specific geological environments. Knowing where to look, and in what kind of rock, is the difference between going home empty-handed and finding a great specimen.
Where to find Weathered Sedimentary Rock
Arid and Semi-Arid Regions
Extensive exposures of sandstone and siltstone in deserts (e.g., Southwestern USA, Sahara Desert, Australian Outback) often display prominent weathering rinds due to physical and chemical weathering processes.
Coastal and Riverine Environments
Cliffs and outcrops along coastlines and river valleys where sedimentary rocks are exposed to cycles of wetting and drying, salt spray, and fluvial erosion.
Mountainous Regions
Exposed bedrock in mountainous areas, particularly in regions with significant temperature fluctuations and freeze-thaw cycles, can exhibit well-developed weathering rinds.
Glacial Terrains
Glacial erratics and bedrock surfaces scoured by glaciers often show weathering rinds that have developed since deglaciation, used in weathering rind dating.
Collecting tips
- Look for Color Changes. The most obvious indicator of a weathering rind is a distinct color difference between the outer layer and the inner, fresher rock. This can be seen on broken surfaces or chipped edges.
- Examine Texture and Hardness. Feel the surface of the rock. Is the outer layer more crumbly, powdery, or, conversely, harder and more resistant to scratching than the interior? This can indicate differential weathering.
- Observe Cross-Sections. Look for rocks that have been naturally broken or chipped, revealing a cross-section that clearly shows the boundary between the altered rind and the unaltered core.
- Consider the Environment. Rocks exposed to the elements for long periods, especially in areas with significant rainfall, temperature changes, or biological activity, are more likely to develop weathering rinds.
Quick Check
- Color:
- Outer layer (rind) typically reddish-brown, yellowish, dark brown, or bleached; inner core reflects original rock color.
- Luster:
- Dull to earthy on the rind; dull to vitreous on fresh interior.
- Streak:
- Varies depending on the dominant secondary minerals in the rind (e.g., reddish-brown for iron oxides) or the primary minerals in the fresh rock (e.g., white for quartz).
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