Very, very cool pictures of Kandovan village in Iran, where the dwellings are carved in to a tuff, which is basically rock made of compressed volcanic ash and other debris.
This of course made me immediately think of the cliff dwellings at Bandelier National Monument, which are carved in to the Bandelier Tuff. Kandovan wins the coolness contest, though, since people are still living in those dwellings.
The site about Kandovan says:
As we have noted previously, in the area of Kandovan, Sahand’s volcanic ash and debris was compressed and shaped by natural forces into cone-shaped pillars containing pockets that became caves.
Off the top of my head, I don’t know if I buy that there would be some factor in the formation of the tuff at Kandovan a bunch of cone-shaped pillars. It’s probably just more of a function of tuff in general that you get those very organic, steeply-sloped shapes when it weathers.
As rocks go, tuff is pretty soft and shockingly light, which is why it’s an ideal rock for people to try to carve dwellings in to. It’s strong and stable enough that undermining it isn’t going to make it collapse, but it’s also much easier to work with than a much harder rock, like granite.
There’s a few pictures I took of the Bandelier dwellings, toward the end of the album from my second New Mexico trip.