Feldspar comes in a lovely variety of stones: moonstone, labradorite, orthoclase, amazonite, sunstone, and spectrolite.
Moonstone displays adularescence, a blue-white opalescence which is a result of light interference with the layered structure of the stone. The most striking example of this is in rainbow moonstone.
Similar yet different, labradorite and spectrolite display labradorescence, “iridescence in metallic hues, called schiller”  with blue and green colors commonly seen, although this effect occurs in all colors.
Pink moonstone and sunstone can also display asterism, typically with four rayed stars.
With all the varieties and colors, feldspar is one of my favorite minerals!
 Gemstones of the World: Newly Revised & Expanded Fourth Edition by Walter Schumann, p.53