Luster is the shine which a pearl displays with an intense brightness. Luster is caused when rays of light are absorbed into and feflect back thin layers of nacre, the semi-opaque layers of calcium carbonate that nake up the pearl. Luster is rated from low to high, wigh high luster resulting when the nacre is thick and well-formed. This causes the pearl to have an inner glow. Also, the quality of the nacre determines the luster.

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Freshwater pearls are grown in mollusks using similar methods as cultured pearls. These mollusks produce off-round oval and rondel shape pearls, and have created a market for fashion pearls jewelry at popular price points. These pearls are similar to the fine Biwa Pearls. Recently, China has beegun producing high qualith round fresh water pearls, similar to the Japanese cultured pearl.