Two sandstone blocks in the Tayma oasis of north-western Saudi Arabia, split down the middle by a fracture so straight it looks laser-cut. Al Naslaa is roughly 6 metres tall, balanced on two narrow pedestals, and has become one of the most photographed geological curiosities on Earth. No laser required. Just stress, time, and wind. The leading explanation is jointing. Sedimentary rock accumulates internal stress as it is buried, compacted, uplifted, and unloaded. When that stress exceeds the tensile strength of the rock, it relieves itself along planar fractures called joints. These form perpendicular to the direction of least principal stress, which is why joints are often strikingly flat and run in parallel sets across entire landscapes. What turned an ordinary joint into Al Naslaa: - A pre-existing plane of weakness, likely a tectonic joint or a softer seam within the sandstone, fixed the fracture geometry - Wind-driven sand acted as an abrasive, scouring the gap and polishing th...