This is at Bua Tong Waterfalls in Chiang Mai, Thailand.
Tried to find scientific information about this waterfall, but google turns up only travellers' vague guesses, suggesting calcium carbonate rich waters. The rock itself seems to have formed by layers of crystallised minerals, and is soft enough to be scratched with a strong stick. It is also quite grippy, allowing tourists to walk up unusually steep surfaces.
What causes such waterfalls and rocks to form, and what are its characteristics?