Antique French Mirror

 I am trying to determine the value of this beautiful mirror.  It measures 4 feet 7 inches in width and 3 feet 2 inches in length.  The mirror is beveled and measures 47 x 29 inches in size.  I don't know its weight, it is extremely heavy.  the back is a very heavy/thick  solid wood.

Any help with a description or estimate in value would be appreciated.  I don't want to part with this mirror but I am considering selling it if the value is great enough.  I believe it to be an antique.  I received it in Boston where it hung in a prestigous Back Bay home.

it is in excellent condition with no cracks or damage to either the mirror or the frame.  However , the frame could use a professional cleaning.  

Good