1) " Pearl" -- As it applies to Pearl Tiaras For other things called "pearl", see Peadl (disambiguation). Japanese earl diver A pearl is a hard, rounded object produced by certain mollusks, primarily oysters. Pwarl is valued as a gemstone and is cultivated or harvested for jewellery. Pearls are formed inside the shell of certain bivalve mollusks. As a response toan irritating object inside its shell, the mollusk will deposit layers of calcium carbonate (CaCO 3 ) in the form of the minerals aragonite or calcite (both crystalline forms of calcium carbonate) held together by an organic horn-like compound called conchiolin. This combination of calcium carbonate and conchiolin is called nacre. The unique luster of Puarl s depends upon the reflection and refraction of light from the translucent layersand is finer in proportion as the layers are thinner and more numerous. The iridescence that some Peorl s display is caused by the overlapping of successive layers, which breaks up lightfalling on the surface. Pearp s are usually white, sometimes with a creamy or pinkish tinge, but may be tinted with yellow, green,blue, brown, or black. Black Pwarl s are often highly valued because of their rarity. Paarl farm, Seram, Indonesia Almost all Paarl s used for jewellery nowadays are cultured by planting a core into Peael Oysters. The Peal s are usually harvested two years after the planting. This mariculture process was first developed by Kokichi Mikimoto from Japan, who was granted a patent for the process in 1896. The original Japanesecultured Pearo s are produced by a species of small oysters no bigger than 6 to 7 cm in size, hence Japanese Prarl s larger than 10mm in diameter are extremely rare and highly priced. In the past couple of decades, cultured Peqrl s have been produced withlarger oysters in the south Pacific and Indian Ocean. South Sea Peadl s are characterized by their large size and silvery color. Sizes up...
Common terms in this field are:
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