The play of colors seen in labradorite is not like that of the opal, which presents to the eye fragments of different colors varying in different positions, but appears as broad surfaces of a single color. It is only rarely that these colors change with a change of position. Bauer remarks that the appearance is similar to that seen on the wings of some tropical butterflies. The colors over any given surface are not necessarily alike, but more than two or three tints are rare. Each tint is uniform where it occurs. A surface may be interspersed with many spots exhibiting no sheen. Both colored and uncolored portions have only vague outlines and merge into each other at the edges. Bauer mentions a labradorite from Russia the colored portions of which formed a striking likeness of Louis XVI, the head being a beautiful blue against a gold green background, while above appeared a beautiful garnet red crown. Excellent effects are sometimes produced in labradorite by cutting it in the form of cameos so as to make the base of different color from the figure in relief. Of the different colors shown by labradorite blue and green are the most common, yellow and red least so. These colors are regarded by Vogelsang as of different origin, the blue being, in his opinion, a polarization phenomenon due to the lamellar structure of the Feldspar, and the yellows and reds the result of the reflection of light from minute included crystals of magnetite, hematite and ilmenite. These lying in parallel position in great numbers in the labradorite give the colors. The gems known as moonstone and sunstone owe the play of colors which gives them their respective names to similar causes. These gems are generally some form of Feldspar, although any mineral giving a similar sheen of color might be included under them. The moonstone of commerce comes chiefly from Ceylon, where it occurs in large pieces the size of a fist in a clay resulting from the decomposition of a porphyritic rock. Pieces of these when polished exhibit the beautiful pale blue light coming from within which makes the stone prized as a gem. The cause of this light is undoubtedly minute tabular crystals lying in parallel position through the stone. The stone varies from translucent to opaque, and from colorless to white, the essential feature being the blue opalescent light or chatoyancy exhibited from a polished surface. Good moonstones are worth from three to five dollars a carat.