Wow. This is an interesting piece. I wish it could talk, or maybe it's best that it stays silent, LOL! The experienced English dealer from whom I bought it thinks that the stone is a Roman Intaglio. There are several of these to be found in England, and there are people who specialize in finding them. Some are set today, and some have original settings (that's rare), and some have been set in Georgian or Victorian times. I believe though it is most likely, and I have asked an expert about this, a 17th century, agate cameo, probably depicting the Holy Family. I personally have never seen diamonds set quite like this either, though the dealer had. I tested the gold on the shank, and it tested a little better than 18 carat. The ring is a size 7 and 3/4 to 8, and it weighs 3.86 grams. The stone is little over 1/2 inch in diameter. I will keep researching and asking experts to learn more about this piece.