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?
Looks like alkali earths ( Ca, Ba , etc.) carbonates deposited from a supersaturated hot spring. As the water emerges from the spring, carbon dioxide leaves the water and the water cools, it precipitates the carbonate ; you could call it limestone. There may be other minerals that will precipitate from a spring. From the foliage , it looks like a relatively recent development.
It's either, as blacksmith37 suggests a Calcite deposit or possibly, given how tectonically active Thailand is, it's Silica from geothermal springs. Geothermal silica often forms large sinter deposits such as the famous Pink and White Terraces, now either destroyed or partially buried at the bottom of Lake Rotomahana, but also much smaller formations in many geothermally active areas throughout the world.
