Hi, the initials seem to be EB but im not sure? The pendant is set in silver and white gold im thinking. The fancy yellow diamond is about 5ctw which is surrounded by 14 peridot. The main diamond has 3 step cuts.
I would suspect it's a citrine, just based on the size, the cut it was given, and the color. You can't tell by one photo, but they don't give diamonds cuts like that.
It's a fun necklace though , sorry I'm not sure who made it
looks like lemon quartz or citrine, but leaning towards the lemon. def not a diamond.
the EB looks like a more personal signing vs a larger jeweler or brand, so I'd assume this wasnt something in large production-- maybe more of a hobbyist or personal project. hope that helps!