A smooth, relatively hard, globular, and generally white gem with a soft iridescent luster, which has from ancient times been used for adornment. (1Ti 2:9; Re 17:4; 18:11, 12, 15, 16; 21:2, 21) It is a hardened mass of calcium carbonate that forms inside oysters and certain other mollusks. When a foreign particle (such as a grain of sand or a small parasite) enters the area between the body and the shell of a mollusk, it  stimulates the creature’s secretion of a calcareous substance called nacre, which hardens into a pearly layer around the irritating intruding material. Successive layers of this shell-like substance are built up around the foreign particle that serves as a nucleus. If the nucleus remains free from the shell because of contractions of the mantle lining the shell, a beautiful pearl is formed in the course of several years.

Pearls of gem quality are taken from the sea pearl oyster, a native of most warm tropical waters, and notably those of the vicinity of Bahrain in the Persian Gulf, and of the Red Sea.

Illustrative Use. The Bible at times alludes to the preciousness of pearls in an illustrative way. With reference to the surpassing value of true wisdom, Job said: “A bagful of wisdom is worth more than one full of pearls.” (Job 28:18) In the Sermon on the Mount, Jesus Christ counseled: “Do not give what is holy to dogs, neither throw your pearls before swine, that they may never trample them under their feet and turn around and rip you open.” (Mt 7:6) Evidently Jesus meant that, if a person shows that he is like a dog or a swine, with no appreciation for spiritual things, one should not further endeavor to share spiritual thoughts and teachings with him. Such corrupt persons would only trample upon valuable spiritual things and abuse or injure anyone endeavoring to share these with them. Jesus also illustrated the preciousness of the Kingdom of the heavens by speaking of “one pearl” of such high value that a traveling merchant seeking fine pearls “promptly sold all the things he had and bought it.” (Mt 13:45, 46) Thereby Jesus showed that an individual appreciating the true worth of gaining the Kingdom of the heavens would be willing to part with everything in order to gain it.​—Compare Mt 11:12; Lu 13:23-25; Php 3:8-11.