Because pearls are natural organic substances they can occur in a wide variety of shapes, many of which are quite unique and interesting.The round pearls you most commonly see are by no means the only shape in which pearls are found!
Indeed, perfectly round pearls (Perlen) are actually quite rare. This is because the eventual shape of the pearl is determined by a number of highly variable factors which occur inside the oyster as the pearl is developing. For example the pearl often assumes the same shape as its nucleus (the irritant which was placed inside the oyster to initiate the formation of the pearl). If the nucleus is not perfectly round, the resulting pearl is likely to reflect this irregularity. In addition the pearl's positioning within the oyster also plays a role in determining its shape. If the pearl develops against the shell, for example, it will become more flattened on that side.
Pearl experts generally divide pearl shapes into three broad categories, based on their overall characteristics:
Spherical shapes are perfectly round or nearly round. They are the "classic" pearl shape that is most familiar.
Symmetrical shapes are are balanced and regular. If you sliced this pearl in half, each half would be a mirror-image of the other half.
Baroque shapes are irregular or abstract. They are non-symmetrical in nature.
Within these three broad categories pearls can be classified into seven basic shapes:
Round: Round pearls are perfectly spherical -- the shape most people think of when they think of a pearl. Because of their relative rarity and "classic" nature they are highly desirable. Round pearls fall into the spherical category.
Near-round: These pearls are not perfectly round. Instead they are slightly flattened or elongated, rather than being a perfect sphere. Nonetheless they are so nearly perfect that they, too, are classified as spherical.
Oval: These pearls are shaped like an oval -- narrower at the ends than they are in the center. Ovals are categorised as a symmetrical shape.
Button: Button pearls are flattened to some degree, making them resemble a button or perhaps a disk rather than a perfect sphere. These pearls are often used in earrings, where the flattened side can be attached to the setting. Buttons are also categorised as symmetrical.
Drop: Drop pearls are pear- or teardrop-shaped.The drop can either be "long" or "short", depending on its proportions. These pearls make attractive earrings or pendants. This is also a symmetrical shape.
Semi-baroque: These pearls are slightly irregular in their shape. For example a pearl which might otherwise be considered an oval, button or drop pearl, but which is not symmetrical in nature, would be considered semi-baroque. Semi-baroque pearls fall into the baroque category of shapes.
Baroque: This is a pearl which is both non-symmetrical and irregular in shape. The baroque pearl can be purely abstract in its shape or it can resemble a cross, stick or some other shape. Baroque pearls fall into the baroque category.
Within these basic categories and definitions there can be many variations. Some Pearls for example develop with one or more grooves or rings encircling them. These pearls are known as ringed or circled. This adjective can be attached to the primary shape in order to more fully describe the pearl, such as "circled round" or "ringed oval."
The shape of the pearl is one of several factors which goes into determining its quality and therefore also its value. In general round and near-round pearls are the most valuable, because of their rarity. Symmetrical shapes are generally considered to be more desirable than baroque shapes. Baroques, however, can be extremely unique, thus increasing their desirability more than might be expected based on their shape alone.