Featured ... I also got a couple interesting RINGS- need STONE EXPERTS, now

I bought a couple of interesting silver rings from the same estate as the brooch/necklaces I posted recently. I need help to ID the stones.
This first ring is Mexican Sterling, with an EAGLE stamp and "CAC" (or "GAC"?). I know most Mexican silversmiths remain unidentified, but- does anyone here have any info or experience with this one?
An unusual feature is the nice all-over toning, with a hint of gold on the outside, and rainbow toning inside! I love that, not gonna touch the patina.

The stone is an oval slice with a mottled pattern that reminds me of a cork-board, only a deeper, amber/orangey brown. My wife guessed moss agate. What say you?



THANX again for everyone's input.

 

Looks more like GAC. Compare it to this mark:

https://www.ebay.com/itm/146644950591

Debora

 

Or GRC?

 

I thought the same, but haven't found any similar marks with "GAC". Your example doesn't have any other similarities, either.
I have seen some with what appears to be a cleaner "CAC" and also the other Mexican marks.

 

Here's another view of that mark:

 

It's just the difference between Guadalajara and Cuernavaca, isn't it?

Debora

 

I am really most interested in what to call the stone...

 

I don't believe so- as far as I know, location initials were only used with the later registration system, nothing to do with the Eagle marking system. Although a location name might be used as part of the maker's mark, that wouldn't seem to be the case, here. "CAC" ought to represent the maker or shop, itself.

 

It's not moss agate.

 

I didn't think so; I just know next to nothing about most stones.

 

Perhaps seam agate? Looks similar to this seller's pieces: ebay.com/itm/356205475673

 

CAG?
https://www.antiquers.com/threads/taxco-sterling-mark-id-tia.936/
Quoting Ladybranch:
"I'm home now and looking through Hougart's The Little Book of Mexican Silver Trade and Hallmarks. [....]
eagle numbers were used by more than one person. In fact the Eagle 3 stamp was probably used by over 300 people. Looking down the longggg list of those using the Eagle 3 stamp, I see no CHM, CIM, or CMM.

Here are the Cs:
CAD, CAG,

 

Thought of often and so missed...

~Cheryl

 

Funny, to me the 1st letter looks more like a "G" than the last one- but searching for "CAG", I found
ebay item #236212997078
These marks look like they do match mine.
Now if only we can ID the stone...

 

Maybe some kind of jasper?

True.

Since Susan already looked in Hougart's (in 2014), I have nothing to add.

Absolutely. Her expertise, kindness, and style are sorely missed