Your camera takes pretty good pics, could you flip the pendant over and take a picture of the numbers on the pendant? & are there more numbers on the necklace it's self? It would be on the clasp or on a tiny plate attached to the clasp.
TL:DR version. I believe with immense conviction that you have there a 12or 13k gold pendant on a gold plated Sterling silver chain.
Here's why:
Alright, I'm wired on coffee and it's after midnight I'm brain dumping what experience I have in 10 years and some of jewelry hunting and making and a guide for the marks I'm not familiar with here, so bare with me... The chain says 925 which leads me to believe it is possibly Gold plate over sterling silver. 925 = 92% silver. Probably plated by a jeweler and not the maker of the chain otherwise it would state the gold content. That's an educated guess. As for the pendant it has an impressive amount of maker's marks and the number 426 on it. That number, 426, is a purity percentage, just like the 925 on the chain. This would put it between 40% and 50% solid gold, the rest of the % being silver most likely. 426= 12k G maybe 13k. My math skills are poo at 12:30 am. :S
Sorry for the barrage of info!
Here are the guides: http://bit.ly/1lzoeP3 http://bit.ly/QtEqUa