Heirloom brooch/necklace

I inherited this brooch/pendant from my mother. It was an anniversary present from my father to her on their 35th. I haven't been able to get it appraised (out of work for 2+ years) and am curious if someone might be able to tell me something about it. I know that the center stone is an emerald; there are some occlusions, not many. The color is exquisite. It is set in a mounting of gold and platinum and there are mined diamonds and chips in the setting. Some are missing. This is a very heavy piece and the gold/platinum work is exemplary. I do not see a makers mark. Sorry for the shoddy photos; I am waiting for my digital SLR to be delivered. Anybody got a clue?

Thanks!
Jane