| 21. | Once that happens, nothing can be done to restore the nacre, he said.
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| 22. | All mollusks can secrete nacre, but oysters do the best job of making pearls.
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| 23. | Layer after smooth layer of nacre in concentric circles around the intruder becomes a pearl.
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| 24. | In nature, pearl oysters produce pearls by covering a minute invasive object with nacre.
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| 25. | These white areas-especially on the pedipalps-have a nacre-like iridescence.
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| 26. | The nacre is white and partly iridescent.
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| 27. | It is green, brown, or black in color with pink to orange nacre.
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| 28. | Researchers there have made an artificial nacre, a composite material that is tough and flexible.
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| 29. | This species was used as the subject in a study of the microscopic development of nacre.
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| 30. | The nacre is thin and the shells are small, making them of little commercial value.
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