The real story behind pearl making
Most gemstones come from the bowels of the Earth, made by pressure and heat over millions of years. But pearls – the most famous biological gems – come from the bowels of mollusks.
âPearl is a word we use for a brilliant creation that a mollusk produces. If debris gets stuck in a mollusk and they cannot remove it, they coat that debris with their own mother-of-pearl or shell material, âsaid Gabriela Farfan, environmental mineralogist and Coralyn W. Whitney stone curator. precious stones and minerals at the Smithsonian’s National Museum of Natural History.
While all mollusks, including oysters, mussels, and clams can technically make pearls, only certain saltwater clams and freshwater mussels are used to commercially cultivate gem-grade cultured pearls.
“Only certain groups of molluscs use a substance, called nacre, which gives gem-quality pearls their opalescent luster,” said Chris Meyer, marine invertebrate zoologist and mollusc curator at the museum.
By collecting and analyzing the pearly pearls, scientists can learn more about how mollusks create these brilliant gems, and how this biological process might change as the Earth’s waters warm.
Gems made by mollusks
Molluscs make pearls as protection against irritants that slip into their soft tissues. They do this by exuding layer upon layer of shell material. For some animals, this material is mother-of-pearl, or mother-of-pearl.
âAll the animal does is put a scab around an intruder, like a grain of sand or a parasite,â Meyer said.
Mother of pearl is a type of crust that gives pearls their pearly luster. But it’s also special for another reason. The material’s recipe, made from organic secretions with a carbon-based mineral known as aragonite, makes it exceptionally strong.
âThese are mineral and organic parts that go together like bricks and mortar,â Farfan said.
This brick-and-mortar process dates back at least 200 million years in the fossil record, but natural pearls are incredibly rare. So, people are now cultivating pearls to do more for the gemstone market.
âThere’s this industry that knows how to handle the production of pearls, which has led to all of these pearl farms,â Meyer said.
Sowing an industry
Farmed or cultured pearls are generally smooth and spherical, due to the way they are made.
âBasically, the pearl farmers very carefully insert a little shell bead into the shellfish. Then they gently put the mollusk back into the ocean or lake and let it grow a pearl for two to five years to harvest it later, âFarfan said.
Since the cultivation process is so efficient, cultured pearls are more widely available than their natural counterparts. So, instead of scarcity, their value comes from their symmetry and brilliance.
âIt’s really the gemologist’s ability to match them that makes them something really special,â said Meyer. “For example, with earrings it’s about how well the pearls match in size and shape.”
Although pearl farming is flourishing today, it faces an uncertain future as do many other aquatic industries threatened by climate change.
Global water temperatures are increasing and local habitats are changing, which will affect mollusks and could threaten all types of bead making.
âMolluscs have optimal temperatures and environmental ranges, like you and I, where their bodily functions work best,â said Stewart Edie, marine paleobiologist and curator of fossil bivalves at the museum. âGlobal warming will alter these ranges, placing animals under stress, so we need to study how this stress affects the energy tradeoffs these animals will have to make. “
Species known to create gem-quality pearls may begin to redirect their energy to other biological needs. For example, the shells of saltwater molluscs weaken due to the acidification of the oceans. These animals might need to spend more nacre to repair their dissolving shells, which means less to trap irritants.
âIt’s not a question of if, but by how much will saltwater pearls be affected by ocean acidification,â Farfan said, âAnd, ocean acidification is just l “One of the big problems that all shellfish face. There are also hurricanes, water quality and pollution problems and so on.”
But by examining the pearls, researchers can see how mollusks react to environmental fluctuations.
âBy using the pearls as mineral ‘time capsules’, we can examine how the environment around the mollusk influenced the pearl and go back to get a better picture of the environmental change,â Farfan said.
Currently, she and other scientists at the museum are studying pearls from freshwater and saltwater bodies to learn more about how their mineralogy evolves under changing temperatures and environments over time. seasons and years.
What they find could help them predict the fate of pearls and mollusks in the future.
âThis is going to give us important information about the impact of environments on these very amazing gems,â said Farfan.
Meet the reef expert who collects environmental time capsules
Say hello to the Smithsonian’s newest shellfish expert
How biominerals are springboards for climate change research
How the world’s largest aquamarine gem was born
Get to know the Guardian of the Hope Diamond