Honestly it's a gorgeous brooch. Sterling silver. Marked CPO in a diamond marking. Stated tokyo, which I'm assuming it's where it was made. It has a center stone which I can't figure out what the stone is. I just did a test. Seems the stone in the middle is Jade.
Bought it from a friend.
A Silver & Grey Chalcedony Brooch, by Inoque Tokyo, probably 1930's,
of urn design with festoon curblink chains and tassel drop, mounted in the centre with an oval grey cabochon stone, reverse stamped SILVER INOQUE TOKYO, with makers initials CPO in lozenge. 3.5" in length.