Antique Glass Top Wooden Desk

I would like to know more about this desk I inherited as I am not sure of its origin or approximate value and was hoping for some assistance.  No one in my family seems to know much about it exept that it is very very old.  It is in fantastic condition and is all original with a great natural greenish patina to it.  The top has a mirrored glass finish that is original as well.  All hand crafted with very little wear for it's age.  There are 3 drawers and 3 wood extensions that slide out.  Pictures really do not do it justice.  There are no markings on it anywhere that would provide a hint of where it comes from. Any help would be greatly appreciated.

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