Like said, can vary massively from OS to OS. Also, what you set during initial import. Either way, your folder should (in "normal/standard" configuration) not just contain an ".vmdk file" but also a ".vbox" and ".vbox-prev" file, as well as a "Logs folder". Now, the last one isn't necessary, though if you haven't removed it, it should have been in your folder. Either way, ".vbox" is definetly necessary.
It's actually a XML file which may be edited with something like Emacs.
Have a nice day,