Thank you Tony and yes, it feels like an important dream.
Something I forgot to mention is that the man also said "you have (or are) taken or taking a lot of pills." The man's manner seemed frantic. The office was dark, dark files on the desk, the desk was dark except for the corner. Also it came to mind that in an office, usually the offices of "power" are in the corners of the building. So the diamond was in the corner of the desk.
Last night I dreamt of white lockers or safe deposit boxes or large rooms...all had numbers. Someone, it was not clear who, told me that mine was 72 and we were on our way to it.