Brooch with Blue Cabochon Marked Sterling

I really need some help with this pin/brooch. I found it the other day and liked it but I have no idea what it is. It can be worn as a brooch or a pendant. It is marked "Sterling: and has the initials C T engraved. I am not sure it this is the maker's initials or the person's who owned it.

Any help would be very appreciated.

Thanks for looking:)