Some definitions:
Physical weathering - Breaking down a rock or mineral by fracturing or abrasion. Relative to feldspar, quartz is much more resistant to physical weathering.
Chemical weathering - Breaking down a rock or mineral (and essentially it is the breaking down of the rock component minerals) via chemical reactions. Quartz is essentially immune to chemical weathering.
Now, both types of weathering are usually happening at the same time, and one will tend to enhance the other. Physically breaking fragments into smaller particles increases the total surface area which enhances chemical weathering. Chemical weathering softens the material which enhances its fracturing and abrasion susceptibility.
Bottom line - It takes a lot of physical wear and tear to destroy a quartz grain.
Now, in the lab, it would be possible to isolate the material from chemical weathering and look at just physical weathering. Say, put 50% feldspar grains and 50% quartz grains in a totally dry tumbler and let it all tumble for a long time. What will you end up with? Rounded quartz grains and relatively small amounts of quartz dust, and feldspar dust. Of course, as mentioned above, that feldspar dust is now in prime condition for chemical weathering to kick in if water based solvents/reactants are introduced.
There are real world examples of (essentially) purely chemical weathered rocks. I'm not going to here get into such much, but see
bauxite and
laterite. In my quick readings of those cites, I didn't notice much specific mention of quartz, but I'm thinking that quartz is not much effected by the process (but I may be wrong).
Moose