Saturday’s talismanic gem: the amethyst. No gems have afforded more interest to the Oriental peoples than those that are known as phenomenal gems; that is, such as exhibit a phenomenal quality, either as a moving line as in the chrysoberyl cat’s-eye, or the quartz cat’s-eye, or as a star, a class represented by the star-sapphire and the star-ruby, all these being considered to bring good fortune to the wearer. A splendid star-sapphire is in the hilt of the sword presented as an Easter gift to King Constantine of Greece, then Prince Constantine, by the Greeks of America, on Easter Day 1913.[438] This ornate and beautiful sword was made by Tiffany & Co. Then there is the alexandrite cat’s-eye which, in addition to its chatoyant effect, changes from green to red, showing its natural color by day and glowing with a ruddy hue by artificial light. The cat’s-eye effect here is caused by a twinning of the crystal; that is, when the gem is cut, with a dome, across the twinning line, this shows itself as a smooth band of white light, with a translucent or transparent space at one side, the line varying in sharpness and in breadth as the illumination becomes more intense. If the light is very bright, the line is no wider than the thinnest possible silver or platinum wire. The quartz cat’s-eye, less distinct than the chrysoberyl cat’s-eye, is also found in the East, and possesses the property that when cut straight across, an apparent striation in the stone produces the cat’s-eye effect, but the material is not so rich or brilliant nor is the gem as beautiful as is the true cat’s-eye. The alexandrite variety of chrysoberyl is colored by chromium and is dichroitic, appearing green when viewed in one direction and red in another; in artificial light, however, the green color is lost and the red alone becomes apparent. The moonstone, with its moonlike, silvery-white light, changes on the surface as the light varies. This is due to a chatoyancy produced by a reflection caused by certain cleavage planes present in feldspar of the variety to which the moonstone belongs. PHENOMENAL GEMS FOR THE DAYS OF THE WEEK Sunday Sunstone Monday Moonstone Tuesday Star sapphire Wednesday Star ruby Thursday Cat’s-eye Friday Alexandrite Saturday Labradorite