It's marked "Handwrought" "Sterling" and "PIIO" or "PIIC" (sorry, I'm old and can't see like I used to). This was given to me by my former mother-in-law, and she bought it in Mexico in the 60's or 70's. It's feels like stone, not glass when I click it against my teeth, but I could be wrong. Thanks so much for your help.
Travertine is more likely, if it doesn't have an eagle mark it dates pre-1948 and that's what they used most often. The gold flecks are confusing though, I've never seen any in the Travertine I've had.
Glass was used a lot then too, almost all the Turquoise from that era is glass, not real.
This is a stumper because the only red I remember seeing from that era was glass but it definitely didn't have flecks and was usually either in a mask shape or had grooves cut in that had silver straps across them.
Pre 48? That is interesting. I really don't know anything about Mexican silver jewelry. I was just thinning out my jewelry collection and realized I hadn't worn this in about 15 years. Here is a (not very good) picture of the back. Now I am thinking I should take a little more time with it. I wasn't going to polish it but thinking now maybe I should?
Looking at the mark now I'm wondering if it is Mexican, their items are marked Mexico in some way 99.99% of the time, I wasn't thinking about it when you mentioned the mark.
Mexicans do sell items from other countries. The chain definitely doesn't look Mexican. That would also explain why the stone is so out of the ordinary for Mex work. If it's not from there then the dating method doesn't work so could be from the time she bought it.
Cleaning up silver is always a good idea. Buffing it with a soft cloth will remove the grunge and tarnish but won't hurt the patina.
Sorry for the bad pictures. I guess they're ok for an auction but not very good for trying to figure out what the heck this stone is. When I posted this, I figured it would be something simple.
Now I am even wondering if I should attempt to sell this. I basically have a necklace of unknown origin, from an unknown time, made with an unknown material. Doesn't really seem like the makings of a great auction ? KWs would definitely be a challenge!