HONEYCOMB WEATHERING OF SANDSTONE OUTCROPS AT AL-HIJRv(MADA'IN SALIH), SAUDI ARABIA
Document Type: Original article
Assoc. Prof. Heritage Resources Management & Tour Guidance dept., College of Tourism & Archaeology, King Saud Univ. Riyadh, Saudi Arabia
In 2008 UNESCO proclaimed Mada'in Saleh as the first Saudi Arabia's world heritage site because of its rock-cut monumental tombs, with their elaborately ornamented façades, of the Nabataeans kingdom. The tombs sandstone outcrops are suffering from honeycomb weathering, which affected the rock surface. Salt weathering often results in the carving of the rock to give a honeycomb appearance. The initial spacing of the hollows may be resulted from the variations in the rocks properties, and weathering creates a roughening of the outcrops rock-cut tombs surface. The lower parts of the rocks surface are flaking of thin, multiple flakes due to salt weathering and repeat wetting and drying of the rock. To determine the mechanism of honeycomb formation at Al-Hijr archaeological site, sandstone samples have been investigated and analyzed by the following methods: field observations (visual examination), Optical Microscope (OM), Polarized Microscope (PM), Scanning Electron Microscope equipped with (SEM-EDS), and X-Ray Diffraction (XRD). The results declared that Al-Hijr sandstones samples have fine to large grained minerals (mono-crystalline and polycrystalline) that different in shape and size. The pore-filling cement is consisting mainly of clay minerals. XRD results revealed that Al-Hijr sandstones mainly composed of Quartz SiO2, Halite NaCl as a salt, Ringwoodite Mg2SO4 and Kaolinite Al2Si2O5 (OH)4. These results represent the correct diagnosis, which will help us to put the suitable strategy of the conservation.
Al-Hijr; Rock-cut tombs; Honeycomb weathering; Investigations; diagnosis
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