Geomorphology of Mountains With Wind only Erosion I am curious what mountains would look like if erosion occurred almost entirely by wind. Specifically, I am curious of how granite mountains would look on a "snowball" terrestrial-sized xenoplanet. 

On a "snowball" world, the planet is earth sized and retains water but it lies outside its sun's "goldilocks zone" and is to cold for liquid water. Ocean's freeze over to a deep of several kilometers with only deep pockets kept liquid by concentrated minerals and vulcanism. 

With no liquid water there will be no liquid erosion and no ice fracturing. The only moisture at all in the air will come from sublimation so very little ice will be deposited at altitude and it likely won't form glaciers or otherwise contribute to erosion. 

At lower altitudes, very slow moving glaciers will probably perform most erosion but at altitude it will be erosion from wind carrying water and CO2 crystals as an abrasive. 

On Earth, erosion from water causes convex (wide rock, narrow erosion channel) while glaciers causes concave (narrow rock, wide erosion channel.) Hard brittle rock such as granite suffers ice fracturing leaving a jagged vertical channels with overall angular features. 

In dry areas on Earth erosion creates rounded, fluid structures like stones shaped by a stream. But I am unclear of how much that is a feature of wind erosion and how much a feature of softer sedimentary stones. It looks like Mars, where erosion is primarily wind driven, does have more rounded and less jagged mountains than on Earth but I don't know about the suspected composition of the those mountains. 

If granite wears from the wind, does it round off or does it's internal structure cause it to fracture even without water? 

Thinking about it another way, if the Earth completely froze over, what would the Rockies, Andes or Himalayas look like after a few million years of wind only erosion?
You do have an earth analogue for this. The Namib Desert in Namibia has been a desert for the past 2 million years with very little precipitation. Also the Atacama Desert is hyperarid since more than 25 million years.

Mars is probably a planet that has below freezing temperatures for million of years, with only wind as an erosional process (apart of a few gravitative processes).

Granite is weathering in roundish forms, as it takes no clear direction from crystallisation. Usually the granite erodes in arid landscapes because of temperature changes and tiny differences in moisture and salts. In a completely frozen plant without a strong atmosphere you would probably still get round forms like Inselbergs.
Furthermore there are of course different kind of forms of wind erosion resulting in strange looking shapes.

High mountain ranges on earth are always limited by erosion from water or glaciers (frozen water) in their growth, as there is more precipitation with altitude.
To get sharp mountains you will need plate tectonics, which will result in the formation of an atmosphere and the release of heat and water (I assume the formation of an atmosphere since platetectonics are associated with volcanismn, which will lead to water and other chemicals like CO2 being released). Thus you will get erosion from water. If the plate tectonics stop and the atmosphere disappears, the mountains will stop growing and there is no moisture left for erosional processes. Then erosion by wind will be the primary geomophological process and the planet could look like Mars.

(I admit this is highly speculative, but the question is speculative in itself.)