Sissy Deas, age 9, of Gastonia, N.C., for her question:

WHAT IS MOTHER OF PEARL?

There's an Arab legend that says pearls are dewdrops filled with moonlight which have fallen into the sea and are swallowed by oysters, and then turned from liquid into solid form. Pearls and the inside of the shells where oysters make the pearls do indeed have the look of moonlight about them.

Mother of pearl is the hard, pearly lining of shells of pearl bearing mollusks, such as the oyster and the abalone.  The substance is also called nacre.

Smooth mother of pearl is made up of many thin, translucent films composed of conchiolin, an organic substance. These films are deposited in irregular but overlapping layers with their edges obliquely exposed to the surface. Light reflected from different levels of this laminated surface produces an iridescent luster characteristic of pearls. Mother of pearl is, as a matter of fact, the same substance found in real pearls.

Mother of pearl is used extensively in the production of fine buttons and jewelry. It has also been used in the manufacture of knife handles.

Another place you'll find mother of pearl used is in the inlaying of furniture and musical instruments. Craftsmen have long been using the inside of certain shells for this type of decoration.

The inner shell lining of nacre, or mother of pearl, is a dull white in some shells while it shines with all of the colors of the rainbow in others. Brighter colors are usually found in the abalone, while a more delicate scale of color is found in the oyster.

Pearls, as a matter of fact, also vary in color. They can be found in dull white to yellow, rose, steel blue and even black. Size, form, texture and color are all important in grading and marketing precious pearls.

While most pearls are round, some are pear shaped or dome shaped. These unusual shapes occur when the pearl becomes attached to the shell before it can reach the round shape for which it is most famous.

Sometimes a parasite will bore through the shell, and in order to protect itself the mollusk will cover the invader with nacre. Created then is what is called a blister pearl. Often it has a hollow center where it covered the parasite. These odd shaped pearls are often made into pendants, brooches and rings. They're not as valuable as pearls, but perhaps just as valuable as much of the fine mother of pearl jewelry items being made today.