To be honest I really do not know, the back behind it is solid metal. If it is it is not like any stones I have seen, I know labradorite, moonstones well...and the only green stones I know of is adventurine and jade and I have never seen speckled jade, it looks solid, so no not jade Im pretty sure, and I can defiantly say its not adventurine, that is kinda like a mint green color. If it did not have the back I could tell better if it was like a rock and could weigh it as well if it were out. Estate items I really just do not know. If it is a stone, I would say it were marble, like the eggs I have had. Other than that, I just always list estate items under costume jewelry. I only check for the metal marks. I never check for stones such as diamonds, ruby's etc unless it is a piece I thought about keeping. Because I have to pay for that at a jewelry shop here in town.
The chain part is very magnetic, like flown to the magnet lol. The bar, lower half that has the symbols and the green stayed still, and know I used a fridge magnet, that is pretty strong, but like I said fridge magnet. Also I always check for gold, so if something is marked, I acid test it as well as then take it to a jeweler. It is gems, I do not have checked. This necklace is not gold. I just do not know about the green center, how old it is, where it was made etc.
I just added two necklaces to the "Estate Find 3 Gorgeous Wide Herringbone Necklaces!!!" auction. You might want to check it out, they are two herringbone, marked 925, one side silver, the other side frosted with three hearts and I love you all the way around it so you can wear it two ways both identical and 18", you might want to check that other auction out :)