Wadi Rum is beautiful desert. Lithologically, it is dominated by two main formations:
- Precambrian granitoid rocks,
- Lower Cambrian to Middle Ordovician quartz sandstones.
Sandstones are formed from cemented grains that may either be fragments of a pre-existing rock or be mono-mineralic crystals. The cements binding these grains together are typically calcite, clays, calcium carbonate and silica.
Sandstone may occur in different colours, depending on admixtures:
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COLOUR OF SANDSTONE
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ADMIXTURE
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yellow
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sulphur
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pink to dark reddish tints (terracotta)
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iron oxide
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blue, dark purple, grey
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manganese
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white
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lack of cement, the sandstone is usually brittle
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There are basically two colour of sandstone in Wadi Rum: Red and White and it changes from West to East. Nature has carved in it amazing landforms, like rock arches, caverns, mushroom rocks and tafoni.
Mushroom rock may be formed in three ways:
- non-uniform erosion and weathering hard mass of sandstone capstone resisted erosion while the underlying softer stone weathered away,
- glacial action - a type of balancing rock. Mushroom is formed from two separate rocks, one of which came to rest on top of the other. Typically, the uppermost rock was transported and deposited by the slow action of a glacier,
- rock disturbance - forms from two rocks, one of which came to rest on the top of the other, caused by a very sudden disturbance such as a rock fall or earthquakes.
Before you log this EarthCache, please answer the following questions using ‘Message this owner’ botton at the top of this page. Do not post your answers in your log.
- What geological process caused the formation of the mushroom?
- What colour of sandstone is the mushroom made of? What kind of mineral it contains?
- Is it typical mushroom shape? What can you say about shape of cross-section of the mushroom stem?
- Describe the surface of mushroom stem.
- Attach photo of yourself or your GPS to your log (black&white or sepia).
Sources and additional information:
- The Sands of Time, The Desert Neolithic Settlement at Ayn Abū Nukhayla, edited by Donald O. Henry (University of Tulsa), Joseph E. Beaver (University of Minnesota Morris), Berlin (2014)
- Sedimentology and depositional environments of the OrdovicianUmm Sahm Sandstone Formation in southern Jordan - Issa Makhlouf, Abdalla Abu Hamad, Basem Moh’d, Arab J Geosci (2017)