Icons Within Apple Apps Disappearing in Mavericks
Not entirely sure what the cause is, but this fixes it for me:


Boot into safe mode by holding shift on boot.
Login to your account.
Restart normally.


There appears to be some sort of caching error and this mechanism also is susceptible to the same fault on older OS as well.



From an Apple Support Communities thread, it seems that it can be fixed for some people by deleting the Dock's Application Support files.

rm ~/Library/Application\ Support/Dock/*.db &amp;&amp; killall -HUP Finder Dock