Rainbow Moonstone definitely the prettiest of the Moonstones.  Color and light shift within the gems iridescence making it appear as if the stone is fluid.  All these rings are designed on a saddle band (thing English riding saddle wide on top, narrow underneath).  A) 1 1/2"long x 1 1/8"wide; B) 1 1/8"long x 1"wide; C) 7/8"long x 3/4"wide; D) 7/8" x 7/8"; E) 1 1/4"long x 3/4"wide.