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  • (intro music)

  • Most of the shiny, bling-y things that we use for jewelry

  • come from deep in the ground, mined from the earth's crust

  • and polished into some of the world's most expensive rocks.

  • But not your grandmother's pearls.

  • As you probably know, those shiny things grew inside the highly calcified bivalve that we know as the oyster.

  • So how did this happen?

  • And why?

  • Whether cultured by humans, or naturally formed in the wild,

  • Pearl formation is the result of a simple irritant.

  • Many species of bivalves, including mussels and clams, are capable of producing pearls when irritated,

  • but only a few can form the shiny coating that makes them so attractive to humans.

  • And oysters do it better than anyone else.

  • In the wild, the irritant is just a small particle that makes its way between the oyster's soft tissue

  • and its hard outer shell.

  • You often hear about pearls starting with a grain of sand,

  • but more often, it's just a random bit of gunk,

  • like a chunk of food that ended up in the wrong place.

  • But, no matter what it is, this foreign object can aggravate the oyster's soft tissues,

  • much as a splinter in your skin, or dust in your eye.

  • So the oyster deals with this irritant first by surrounding it with a thin layer of protective cells,

  • forming what's called a pearl sac.

  • These cells then secrete a combination of proteins

  • that form a kind of molecular glue around the offending bit of grit.

  • The sac then starts releasing layer after layer of material called nacre.

  • Also known as mother of pearl, nacre is mostly composed of a crystallized form

  • of calcium carbonate called aragonite.

  • Chemically speaking, it's the same compound as the oyster's shell,

  • but that kind of calcium carbonate, called calcite, is more durable and arguably less lovely.

  • Inside the pearl sac, the aragonite bonds with the base layer of protein glue,

  • and then the layers start to stack up.

  • These layers of nacre will give the pearl its iridescence.

  • But despite their smooth, glossy appearance, they actually have a slightly jagged texture.

  • Scientists think this allows the pearl to be rotated easily by the flowing water, which in turn allows

  • the coating to be distributed evenly.

  • And since the irritant itself was probably irregular in shape and shifted around while it was being coated,

  • most pearls aren't perfectly round.

  • The ones that are have usually been cultured by humans,

  • and those are made by implanting oysters with bits of tissue from other oysters,

  • and sometimes, spherical beads, to stimulate the formation of a pearl sac.

  • Often in the oyster's gonad, where the oyster can't dislodge whatever has been put there.

  • That sounds pretty irritating.

  • Thanks for asking, especially to our Subbable subscribers who keep these answers coming.

  • If you have a quick question, let us know on Facebook or Twitter or in the comments below,

  • and don't forget to go to and subscribe.

  • Subtitles by Skylar Coland via Amara

(intro music)


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B2 中高級

牡蠣是怎麼做珍珠的? (How Do Oysters Make Pearls?)

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    NNN 發佈於 2021 年 01 月 14 日