진주조개 (Pinctada fucata) : 진주를 만드는 대표적인 연체동물, 체내에서 진주 성분을 분비해 천연 진주를 만듬
진주층(Nacreous layer)
1. 특징
체내에서 분비하는 진주 성분으로 조개 속에 침입한 이물질로부터 몸을 보호하기 위해 분비하는 물질이다. 진주조개껍데시의 가장 내부 층과 구조적으로 동일하다. 쉽게 부서지지 않고 탄성을 가진다. 껍질이 파열되는 것을 방지해 내부의 부드러운 몸을 포식자와 기계적 손상으로부터 보호하는 역할을 한다.
+ 능주층(Prismatic layer) : 조개껍데기의 외부를 구성
2. 구성
95% 이상이 탄산칼슘(석회질)미네랄로 구성되어 있다. 5%의 이하의 소량의 유기물을 포함한다. 유기-무기 복합형태를 이루며 그 구조는 복잡하고 유기적인 계층구조를 가진다. 이러한 독특한 구조를 통해 진주층은 에너지를 효율적으로 흡수한다. 파괴인성은 순수한 탄산칼슘보다 백 배 에서 천 배가량 높다. 생명체는 이런 복잡한 유무기 복합소재를 형성하기 위한 모든 과정을 정교하게 조절하는데, 이를 '바이오미네랄화' 또는 '생광물화'라고 한다.
+Nacre is composed of calcium carbonate, in the form of mineral aragonite and calcite and the proteins conchin and perlucin which form a substance known as conchiolin that more or less functions as the "glue" that holds the layers together. mineral aragonite has a crystal structure, the conchiolin is very porous.
진주의 형성 과정
1. Some foeign body, such as sand, a parasite or some other organic material manage to make its way inside the oyster's shell
2. They come in contact with mantle, a layer that protects the oyster's internal organs, sometimes even damaging it.
+External damage to the shell itself that results in damage to the mantle will also trigger
3. The mantle begins to depsoit a substance called nacre, also called mother of pearl, onto it.
4. The oyster will apply several layers of nacre to the foreign body of the invading body being one potential contributing factor to the ultimate shape of the pearl.
Natural pearls 특징
Natural pearls are nearly 100% calcium carbonate and conchiolin. It is thought that natural pearls form under a set of accidental conditions when a microscopic intruder or parasite enters a bivalve mollusk and settles inside the shell. The mollusk, irritated by the intruder, forms a pearl sac of external mantle tissue cells and secretes the calcium carbonate and conchiolin to cover the irritant. This secretion process is repeated many times, thus producing a pearl. Natural pearls come in many shapes, with perfectly round ones being comparatively rare.
Typically, the build-up of a natural pearl consists of a brown central zone formed by columnar calcium carbonate (usually calcite, sometimes columnar aragonite) and a yellowish to white outer zone consisting of nacre (tabular aragonite). In a pearl cross-section such as the diagram, these two different materials can be seen. The presence of columnar calcium carbonate rich in organic material indicates juvenile mantle tissue that formed during the early stage of pearl development. Displaced living cells with a well-defined task may continue to perform their function in their new location, often resulting in a cyst. Such displacement may occur via an injury. The fragile rim of the shell is exposed and is prone to damage and injury. Crabs, other predators and parasites such as worm larvae may produce traumatic attacks and cause injuries in which some external mantle tissue cells are disconnected from their layer. Embedded in the conjunctive tissue of the mantle, these cells may survive and form a small pocket in which they continue to secrete calcium carbonate, their natural product. The pocket is called a pearl sac, and grows with time by cell division. The juvenile mantle tissue cells, according to their stage of growth, secrete columnar calcium carbonate from pearl sac's inner surface. In time, the pearl sac's external mantle cells proceed to the formation of tabular aragonite. When the transition to nacre secretion occurs, the brown pebble becomes covered with a nacreous coating. During this process, the pearl sac seems to travel into the shell; however, the sac actually stays in its original relative position the mantle tissue while the shell itself grows. After a couple of years, a pearl forms and the shell may be found by a lucky pearl fisher.[11]
Cultured Pearls 특징
Cultured pearls are the response of the shell to a tissue implant. A tiny piece of mantle tissue (called a graft) from a donor shell is transplanted into a recipient shell, causing a pearl sac to form into which the tissue precipitates calcium carbonate. There are a number of methods for producing cultured pearls: using freshwater or seawater shells, transplanting the graft into the mantle or into the gonad, and adding a spherical bead as a nucleus. Most saltwater cultured pearls are grown with beads. Trade names of cultured pearls are Akoya (阿古屋), white or golden South sea, and black Tahitian. Most beadless cultured pearls are mantle-grown in freshwater shells in China, and are known as freshwater cultured pearls.
Natural Pearl과 Cultured Pearl의 구별 방법
Cultured pearls can be distinguished from natural pearls by X-ray examination.[12] Nucleated cultured pearls are often 'preformed' as they tend to follow the shape of the implanted shell bead nucleus. After a bead is inserted into the oyster, it secretes a few layers of nacre around the bead; the resulting cultured pearl can then be harvested in as few as twelve to eighteen months.
When a cultured pearl with a bead nucleus is X-rayed, it reveals a different structure to that of a natural pearl (see diagram). A beaded cultured pearl shows a solid center with no concentric growth rings, whereas a natural pearl shows a series of concentric growth rings. A beadless cultured pearl (whether of freshwater or saltwater origin) may show growth rings, but also a complex central cavity, witness of the first precipitation of the young pearl sac.[12]
Freshwater and saltwater pearl
1. Freshwater pearl : Freshwater pearls form in various species of freshwater mussels which live in lakes, rivers, ponds and other bodies of fresh water. These freshwater pearl mussels occur not only in hotter climates, but also in colder more temperate areas such as Scotland.
2. Saltwater pearl : Saltwater pearls grow within pearl oysterswhich live in oceans. Saltwater pearl oysters are usually cultivated in protected lagoons or volcanic atolls.
단어
patent : 특허
bivalve : 이매패류
mollusk : 연체동물
irritate : 짜증나게 하다, 괴롭히다
secrete : 분비하다
nacre : 자개
columnar : 기둥 모양의
Displacement : 바꾸어놓기
rim : 가장자리
Embed : 깊숙이 넣다, 끼워넣다
sac : 주머니
tabular : 표의, 반반한 판자 모양의
shell : 껍데기
transplant : 이식하다
recipient : 받아들이는
precipitate : 침전물
gonad : 생식선
bead : 구술
implant : 이식하다
concentric : 중심이 같은 집중적인
cavity : 공동
출처 : 차형준, “바다의 보석", 포항공대신문, 2018.03.28, http://times.postech.ac.kr/news/articleView.html?idxno=20104
출처 : How and Why Do Oysters Make Pearls?, Today I Found Out, Youtube, 2016.05.10, https://www.youtube.com/watch?v=0O33I5g_t-8
출처: Pearl, Wikipedia, https://en.wikipedia.org/wiki/Pearl#Freshwater_and_saltwater_pearls