The first thing to do is to look on the clasp and on the back of the pendant for the words and numbers 14k, 10k, 18k or 585, 750 and any maker's names, letters or logos. Let me know what you find or take photos and add them here using the ADD FILES button and we can go from there.
Refrain from rating me until I have finished answering and after I get more information from you.
This piece looks to be 10k or 14k gold with seed pearl in the center and two round brilliant cut blue topaz lavaliers. The style of the pendant dates the piece to 1910 to 1915 when seed pearls and drop features were popular in jewelry. These features were also popular again in the 1940's, but the life of your grandmother(s) would help you determine the timeline of this piece from those two date ranges. This pendant as antique gold jewelry has a value of $475.00.
Since I cannot see the markings or test the piece for gold purity, I would suggest that you take it to a small, hometown jeweler to verify that it is gold-something only a physical inspection can do at this point since you can't find the marks we are looking for (they are probably there, but it takes a jeweler's loupe to see on some pieces). The secondary price if the piece is NOT gold would $75.00 as a piece of antique costume jewelry.
Please do click the stars to rate me, thank you!
This looks to be an American piece of jewelry. Especially if you end up finding a 14k or 10k mark somewhere in addition to the marks you have described. I am thinking that the 90x SXR is going to end up reading 14k and a maker's initials once the tarnish is cleaned.