{"id":15769,"date":"2022-04-18T09:00:47","date_gmt":"2022-04-18T07:00:47","guid":{"rendered":"https:\/\/www.discoverwildlife.com\/?p=60202"},"modified":"2022-04-18T09:17:14","modified_gmt":"2022-04-18T07:17:14","slug":"pearls-what-lies-behind-their-beauty","status":"publish","type":"rss_feed","link":"https:\/\/c01.purpledshub.com\/bbcwildlife\/rss_feed\/pearls-what-lies-behind-their-beauty\/","title":{"rendered":"Pearls: what lies behind their beauty?"},"content":{"rendered":"

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By JV Chamary\n \t\t<\/p>

Published: Monday, 18 April 2022 at 12:00 am<\/p>

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Pearls are organic mineral deposits that have been valued as precious gemstones throughout human history.\u00a0They\u2019re made by various molluscs, including snail- like gastropods such as abalones, but the majority of commercial pearls are harvested from bivalves (two-shelled molluscs), such as marine oysters<\/a> and freshwater mussels.<\/p>\n

What is a pearl made of?<\/h2>\n

The same materials used in a shell, the mollusc\u2019s exoskeleton. Shells consist of the mineral calcium carbonate in an ordered arrangement to form a crystal, of either calcite or aragonite, and a matrix of organic molecules that includes a key protein called conchiolin. The crystals are layered and make up more than 95% of a pearl or shell.<\/p>\n

What\u2019s the difference between pearls and shells?<\/h2>\n

Besides overall shape, they differ in how their layers are deposited. The materials that make up a shell are secreted by the mantle, a large multi-purpose organ on a mollusc\u2019s back. A shell can include three concentric layers made by different zones of the mantle: an inner layer called nacre, a porcelain-like \u2018prismatic\u2019 middle layer, and a protein-rich outer layer with \u2018skin\u2019 (periostracum).<\/p>\n

Within a \u2018pearl sac\u2019, these same layers are deposited in the opposite order to that of the shell, so pearls are basically inside-out shells with nacre on the outside. Comparing mantles and pearl sacs shows they\u2019re made using the same genetic instructions \u2013 there are no special genes for making pearls.<\/p>\n

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Pearl hidden inside of oyster. \u00a9 Maciej Toporowicz, NYC\/Getty<\/em><\/span><\/figcaption><\/div>\n

How does a pearl form naturally?<\/h2>\n

Contrary to popular belief, pearl formation is not normally triggered by a foreign object, such as a grain of sand. Instead, pearl formation typically begins after an injury that transports cells of the shell- forming mantle to an abnormal location (for example when the shell is pierced or\u00a0a parasite burrows into a mollusc\u2019s body). Those relocated cells then divide and develop into a \u2018pearl sac\u2019. Natural pearls are incredibly rare.<\/p>\n

How are artificial pearls produced?<\/h2>\n

Cultured pearls are produced by humans transplanting mantle cells from a donor animal into another individual. The donor cells can even be put into a closely related species without tissue rejection by the host\u2019s immune system.<\/p>\n

Few natural pearls are a perfect sphere, but mantle tissue is often inserted with a spherical bead around which its minerals are deposited \u2013 an artificial pearl forms around that nucleus and its nacre is just an outer shell, whereas a natural pearl is made of shell alone. It takes at least a year before cultured pearls can be harvested.<\/p>\n

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Pearls are often strung together to form necklaces. \u00a9 MoMo Productions\/Getty<\/em><\/span><\/figcaption><\/div>\n

What is mother-of-pearl?<\/h2>\n

It\u2019s the common name for the nacre or \u2018nacreous layer\u2019 that causes a pearl\u2019s surface to reflect light while giving it a translucent lustre. That pearlescent quality is arguably the most beautiful feature, but some pearls have little to no nacre, so they appear smooth and chalky.<\/p>\n

Such \u2018non-nacreous\u2019 pearls include the largest natural pearl certified by the Gemological Institute of America<\/a>: the Giga Pearl, which was formed by a giant clam, weighs 27kg and has an estimated worth of up to US$200 million (approximately \u00a3150 million).<\/p>\n

Mother-of-pearl is sometimes used in architecture, furniture and statues, and antique mother-of-pearl items can be collected<\/a>.<\/p>

What creates a pearl\u2019s colour?<\/h2>\n

Nacreous pearls can be anything from silver-white or orange to green or black (pink is the most desirable). Like the blue- on-brown eyes of peacock\u2019s tail, a pearl\u2019s\u00a0colour isn\u2019t due to pigments, but how its structure scatters light at a sub-microscopic level. In fact, the scientist who first observed organisms under a microscope\u00a0in 1665, Robert Hooke, noted that peacock feathers consist of thin plates that resemble pearlescent shells.<\/p>\n

Similarly, a pearl gets its \u2018structural colour\u2019 from tablets of aragonite crystals and conchiolin sheets within\u00a0nacre: the tablets are stacked in a brick- wall pattern, which causes light particles (photons) to bounce around internally\u00a0at a pearl\u2019s surface \u2013 between crystal\u00a0layers \u2013 like pinballs in a machine before the light reaches your eyes.<\/p>\n

That scattering influences how light is transmitted, creating a colour filter, so a pearl\u2019s appearance depends on the thickness of crystal layers in its nacre.<\/p>\n

Main image: Halved fresh oyster with oyster pearl. \u00a9 ImageBROKER\/Alamy<\/em><\/p><\/body><\/html>\n

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By JV Chamary Published: Monday, 18 April 2022 at 12:00 am Pearls are organic mineral deposits that have been valued as precious gemstones throughout human history.\u00a0They\u2019re made by various molluscs, including snail- like gastropods such as abalones, but the majority of commercial pearls are harvested from bivalves (two-shelled molluscs), such as marine oysters and freshwater […]<\/p>\n","protected":false},"author":24,"featured_media":15770,"template":"","categories":[1],"acf":{"readingTimeMinutes":"4"},"uagb_featured_image_src":{"full":["https:\/\/c01.purpledshub.com\/uploads\/sites\/44\/2022\/04\/pearls-what-lies-behind-their-beauty-scaled.jpg",2560,1707,false],"thumbnail":["https:\/\/c01.purpledshub.com\/uploads\/sites\/44\/2022\/04\/pearls-what-lies-behind-their-beauty-150x150.jpg",150,150,true],"medium":["https:\/\/c01.purpledshub.com\/uploads\/sites\/44\/2022\/04\/pearls-what-lies-behind-their-beauty-300x200.jpg",300,200,true],"medium_large":["https:\/\/c01.purpledshub.com\/uploads\/sites\/44\/2022\/04\/pearls-what-lies-behind-their-beauty-768x512.jpg",768,512,true],"large":["https:\/\/c01.purpledshub.com\/uploads\/sites\/44\/2022\/04\/pearls-what-lies-behind-their-beauty-1024x683.jpg",800,534,true],"1536x1536":["https:\/\/c01.purpledshub.com\/uploads\/sites\/44\/2022\/04\/pearls-what-lies-behind-their-beauty-1536x1024.jpg",1536,1024,true],"2048x2048":["https:\/\/c01.purpledshub.com\/uploads\/sites\/44\/2022\/04\/pearls-what-lies-behind-their-beauty-2048x1365.jpg",2048,1365,true]},"uagb_author_info":{"display_name":"importmanagerhub@sprylab.com","author_link":"https:\/\/c01.purpledshub.com\/bbcwildlife\/author\/importmanagerhubsprylab-com\/"},"uagb_comment_info":0,"uagb_excerpt":"By JV Chamary Published: Monday, 18 April 2022 at 12:00 am Pearls are organic mineral deposits that have been valued as precious gemstones throughout human history.\u00a0They\u2019re made by various molluscs, including snail- like gastropods such as abalones, but the majority of commercial pearls are harvested from bivalves (two-shelled molluscs), such as marine oysters and freshwater…","_links":{"self":[{"href":"https:\/\/c01.purpledshub.com\/bbcwildlife\/wp-json\/wp\/v2\/rss_feed\/15769"}],"collection":[{"href":"https:\/\/c01.purpledshub.com\/bbcwildlife\/wp-json\/wp\/v2\/rss_feed"}],"about":[{"href":"https:\/\/c01.purpledshub.com\/bbcwildlife\/wp-json\/wp\/v2\/types\/rss_feed"}],"author":[{"embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcwildlife\/wp-json\/wp\/v2\/users\/24"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcwildlife\/wp-json\/wp\/v2\/media\/15770"}],"wp:attachment":[{"href":"https:\/\/c01.purpledshub.com\/bbcwildlife\/wp-json\/wp\/v2\/media?parent=15769"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcwildlife\/wp-json\/wp\/v2\/categories?post=15769"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}