Here is a beautiful blue/green medoum size Rainbow Moonstone setnin a one of Art Nouveau Ring design.
Rainbow Moonstone is actually a labradorite. This is one of my favorite designs and can be replicated in your choice of gemstone by clicking on the "Request Custom Order" button.
This ring is a size 7 1/2 but can be sized from a 5 up to a 9.
The stone used here is a 15 by 12 mm oval cabochon. (about 5/8 by 1/2 inch ).