The stone is a square citrine. Now citrines can range from the insipid pale yellow to the richest of ambers, and this one is the colour of pure sunshine.
I cut out a dainty little heart shape on each side of the bezel to let more light into the back of the stone.
I seem to be having a run on square shapes of late. The last ring I finished was a lab created alexandrite. I don't usually go for lab created stones but this one even has the same colour change properties found in the natural stones. It changes between green and pink depending on the type of light.