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 rock’s properties, and weathering creates a roughening of the
outcrops rock-cut tombs surface. The lower parts of the rock’s 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.