|Amazonite is a blue to blue-green variety of feldspar that is usually translucent to opaque. It most often cut in to cabochons. It tends to show an elongated grain direction and often in a combination with other minerals. The color is radiation induced and the colored varieties contain Pb.
Moonstone is clear to peach colored feldspar that shows the optical property known as "adularescence". This is a billowy light that appears to ride over the surface or interior of the stone. It is caused by the layered structure of the feldspar which produces a light interference pattern throughout the stone. It sometimes looks like a cats-eye in on the surface of the stone.
Labradorite is a dark blue to gray-black feldspar that shows its characteristic light play called "labradorescence". This phenomena appears similar to the surface sheen seen when an oily residue floats on water. It produces a full spectrum of shimmering colors that change as the stone is tilted. Again this coloration comes from disjoints in the crystalline structure of the stone. The lamellae are often found in reverse orientations produces the light break up.
Sunstone gets it color effect from a "schiller" effect caused by the break up of light by small particles suspended in the feldspar. In the case of sunstone (from Oregon) the schiller effect comes from small amounts of metallic copper in the crystal lattice. This causes multiple internal reflections and make some of the stones appear to glow an orangish color. Even smaller dispersed copper may impart a reddish or greenish color to the stone without the schiller effect. These stones are often cut into faceted stones. Other sunstone feldspars come from India and Africa and their schiller may be caused by other contained minerals.
Orthoclase can be found as transparent gemstone in light straw to darker yellow colors. It is faceted to nice stones and they are available to pretty good size. Due to its lower hardness it does not wear well in rings but should be used in necklaces and ear-rings. The coloration comes from Fe impurities.