After I asked the question, the [Rosetta mission][1] sent back some glorious images of rocks as jagged as those on any science fiction book cover:

![enter image description here][2]

I suppose the difference is that these are on the surface of a comet, which, unlike the Moon, is geologically active. 

These are hardly what you'd call mountains - the whole nucleus is only 4km long, so the features shown must be hundreds of metres in size at best. But still, I would imagine freshly formed mountains would look something like this in the absence of erosion.

It never rains but it pours. Here is a glorious photo of mountains on Pluto from NASA's New Horizons mission, from September 2015. Pluto is another (surprisingly) geologically active world, with apparently little erosion. These ones really are mountains, about three kilometres in height. They are probably made of water ice rather than rock, which is very hard at those temperatures. They also apprear very jagged.

[![enter image description here][3]][3]

I conclude from this that mountains on active worlds without erosion will generally appear jagged; the smoothness of the Moon's mountains is not due to the absence of erosion - rather, they're smoothed *because* of erosion, which in the Moon's case is primarily due to micrometeorites and takes place over a very long time. This is possible because the Moon is not geologically active, so its mountains are far older than the ones in the pictures above.

Finally, I can't resist editing again to add another image from the Rosetta mission, taking during the spacecraft's final descent before a controlled collision with the comet in September 2016. It's just an incredibly beautiful image. ([source][4])

[![enter image description here][5]][5]


  [1]: http://www.esa.int/Our_Activities/Space_Science/Rosetta
  [2]: https://i.stack.imgur.com/yC6tY.png
  [3]: https://i.stack.imgur.com/HBSP3.png
  [4]: https://twitter.com/tedstryk/status/781702192772313092/photo/1?ref_src=twsrc%5Etfw
  [5]: https://i.stack.imgur.com/aQq0I.jpg