Pearls are unique in the gem world in that they are made by living creatures rather than being mined from the earth. When an irritant is introduced (accidentally or intentionally in the case of cultured pearls) into a shellfish like a mollusk. In order to better tolerate the irritant, the mollusk coats the pearl with layers of a hard, smooth substance called nacre (rhymes with "acre") that mollusks have coating their shells--these shells are commonly known as mother-of-pearl.

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Large photos are nice, so you can see up close the designs. Very pretty project ideas and the beginning of the book has a good intro for those just starting to "get into" pearls. Would definitely recommend.