Here is a full light blue flash rainbow moonstone ring set in a medium gage sterling silver art nouveau split shank ring design.

The stone used here is a 18 by 12 mm rectangle shaped cabochon or about 3/4 by 1/2 inch.

This ring is a size 7 1/2 but can be sized from a 5 to a 9.

Rainbow Moonstones can vary with regard to the floating color you see in the stone. Most have a predominant blue sheen but this can vary and have other colors as well.

Rainbow Moonstone is actually more specifically a labradorite. Traditional moonstones belong to the orthoclase feldspar group while rainbow moonstone comes from the labradorite feldspar group. Another proper name for Rainbow Moonstone is “spectralite”
Both Labradorite and Moonstone are close cousins.