From Seabed to Summit
The striking fins of rock that define the Phou Asa summit are made of quartzite, a stone with a history that begins as humble sand. Hundreds of millions of years ago, during the Paleozoic Era, this entire region was a shallow sea. Rivers deposited quartz-rich sand onto the seafloor, which over time compacted into thick layers of sandstone.
This sandstone did not remain unchanged. As it was buried deeper within the Earth's crust, intense heat and pressure transformed it through a process called metamorphism. The individual quartz sand grains recrystallized and fused together, eliminating the original spaces between them and forming an incredibly dense, interlocking crystal structure. This new rock, quartzite, is exceptionally hard, registering a 7 on the Mohs hardness scale, and far more resistant to weathering than its parent sandstone. Durability is why, after millions of years of erosion have worn away softer surrounding rocks, these quartzite ridges remain standing.