CHATOYANCY
Chatoyancy is the silk like appearance known from such minerals as tiger’s eye or crocidolite. In pearls the term has been applied to porcelainous pearls such as those from the snails Strombus and Melo, whose surfaces exhibit flame-like markings. The conch shells themselves sometimes display the same property. This effect is due to the structure of these non-nacreous pearls. Conch pearls are formed of concentric layers of fibrous or prismatic crystals rather than nacreous crystals. The flamelike or moiré pattern is an optical effect that results from the arrangement of these prismatic crystals perpendicular to the surface of the pearl.
ORIENT
Orient is best defined as iridescence or the play of rainbow colors across the surface of a pearl. It differs from luster, although the two terms are sometimes used interchangeably. The term probably originated from the fact that orient, or iridescence is best seen by rotating a pearl to align it in different positions. Another possibility is that the term stems from the original Latin meaning of oriens, “the rising of the sun”. The same criteria that determine the intensity of luster also influence the quality of orient. The predominant factors are the thickness of the nacre and the regularity of the component nacreous crystals. Multiple layers of consistently thin nacre, composed of perfectly formed nacreous crystals, produce the finest orient. The surface quality of the pearl and the amount of conchiolin also affect the orient. Smooth, non-pitted either composed entirely of nacre or, if cultured, with thick outer layers of nacre exhibit the best orient. Pearl made up of mostly conchiolin do not show any orient.
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