Coral, the English name of coral, comes from the Latin Corrallium. Coral is one of the important organic gemstones, and it is also a favorite gemstone variety at all times and at home and abroad. The ancient Romans believed that coral had the functions of preventing disasters, giving people wisdom, stopping bleeding and driving away heat. Closely related to Buddhism. Buddhists in India, China and Tibet regard red coral as the incarnation of Tathagata. They regard it as a mascot for offering sacrifices to the Buddha, and it is often used to make beads or decorate statues. This is a very precious jewel.
Coral is a kind of marine cylindrical coelenterate named "Coral". In the white larval stage, it is automatically fixed on the calcareous remains of ancestral corals. Corals rely on tentacles to catch food and secrete calcium (calcite is a mineral component) to build their own bodies. In the process of coral growth, in order to catch more food and absorb sunlight, it not only grows upward, but also expands forward, backward and left and right, forming a three-dimensional dendritic biota. Just take out a bunch, elegant and beautiful, and it is a natural work of art.
The chemical composition of coral is mainly CaCO3, which exists in the form of microcrystalline calcite aggregate with a certain amount of organic matter. Most of them are dendritic with longitudinal stripes on them. Each coral has concentric circles and radial stripes in its cross section. The color is often white, but there are also a little blue and black. Gem-grade corals are red, pink and orange. Red is formed because coral absorbs about 1% iron oxide in seawater during its growth, and black is formed because it contains organic matter. It has glass luster to waxy luster, opaque to translucent, and the refractive index is 1.48- 1.66. The hardness is 3.5-4, the density is 2.6-2.7g/cm3, and the density of black coral is relatively low, which is 1.34g/cm3. Sexually fragile. Strong foaming in hydrochloric acid. No fluorescence.
Species, evaluation and purchase of corals. Coral species include red coral (called "bovine blood" and "angel hair" abroad), black coral, blue coral, Mediterranean coral, Japanese coral, Cameroonian coral and China Hainan coral. The quality of corals is similar, and the color and fragmentation are the basis of economic evaluation and purchase. Colored ones are of higher quality than white ones, and the colors should be beautiful, bright and pure. The bigger the block, the better. The value of coral is also influenced by local customs, for example, Arabs prefer bright red, while pink is popular in Europe.
Coral imitation and identification. (1) Dyed marble: uniform red, granular structure, no concentric structure in section, no uniform stripes. Wipe with a cotton swab dipped in acetone, and the cotton swab appears red. (2) Pink glass: glass luster, bubble-containing, conchoidal fracture, no bubble in hydrochloric acid. (3) Pink plastic: it does not have the unique banded structure of coral, but it has traces left by using the mold, and does not foam when it meets hydrochloric acid. (4) "gilson" synthetic coral: fine-grained structure, no banded structure, slightly different in color or transparency from natural coral, with a density of 2.45g/cm3, which is smaller than natural coral.
Corals with good shapes are often used as ornamental stones, and can also be used as raw materials for carving works of art or processed into necklaces, rings, bracelets, brooches and earrings. Coral can be used as medicine, and "coral medicated wine" is an excellent tonic, which can perspire and diuresis.
Coral protection. Because the chemical composition of coral is CaCO3, its chemical properties are unstable. People should not wear coral necklaces for a long time when sweating in hot summer, because the salt and acid secretions in sweat will corrode corals. Coral should not touch cosmetics, perfume, alcohol, salt, oil and vinegar. Coral structure is not dense, porous and easy to get dirty. Use neutral soapy water when cleaning.
Corals are produced in warm marine areas, and reef-building corals grow in relatively shallow warm coastal waters, usually 30 meters away from the water surface, and grow most vigorously. The Mediterranean Sea is a famous producer of coral gems. The red sea element in Africa is famous for its numerous coral reefs. In addition, there are high-quality corals in the waters from Ogasawara Islands to Spanish Iwo Jima, Keelung in Taiwan Province Province of China and Penghu Islands!
Coral belongs to the phylum Vertebrata, and its characteristic is that it has vertebrates, and its body has two germ layers, and the inner and outer germ layers are separated by mesoderm, which are radially symmetrical. Its life history has the phenomenon of generation alternation, which can be roughly divided into hydra period and hydra period. Except hydra corals, living corals have only a short hydra period, and both stony corals and soft corals have only a hydra period. Most corals live in groups. Groups are formed by asexual budding or fission propagation of individuals, and the number of individuals in each group is different.
Coral is an animal. From a biological point of view, coral is a group of organisms formed by the aggregation of many corals (corals) (but a few corals are single corals). Taxonomically, corals belong to the phylum coelenterata. According to the characteristics of bones, it can be divided into stone corals and soft corals. Rock corals have the ability to secrete calcium carbonate to form hard masses, mostly reef-building corals; Soft coral does not secrete a lot of calcareous bones, but supports the body with calcareous bone needle bundles.
As far as the shape of coral is concerned, there are branches, brains, trees, strips, sheets, spirals and so on. Environmental factors affecting coral growth are luminosity, temperature and ocean current. Reef-building corals usually grow in shallow water because they need sunlight to grow; In terms of temperature, the optimum growth temperature is between 23 and 28 degrees, below 18 degrees and above 30 degrees, which is not conducive to coral growth. Too strong currents or waves can also cause mechanical damage to corals, so typhoons and storms often cause serious damage to coral reefs. The growth rate of coral varies with species, age and place.
Coral reproduction can be divided into asexual reproduction and sexual reproduction. Asexual reproduction includes germination, rupture, emergence and so on. As for sexual reproduction, it includes in vivo and in vitro fertilization. In vitro fertilization, coral excretes sperm and eggs about six or seven times, with a few minutes interval each time. After three days, fertilized eggs can start swimming, and larvae have phototaxis and can move in the surface water layer. At this time, if suitable substrate is provided, the larvae can continue to grow abnormally. In the aspect of in vivo fertilization, fertilized eggs remain in the mother's body and develop into floating larvae, which are then released by the mother; The release time of floating wave larvae varies with species and regions. Coral floating larvae have cilia on the surface, which can help swimming, so whether floating or crawling, there will be a floating period to find a suitable growth environment. Most coral floating larvae form new individuals through attachment and metamorphosis. A few people are free all their lives, so they directly transform into new individuals without attachment.
Coral is distributed in warm ocean currents, at the bottom of shallow water, which is the masterpiece of a coelenterate called coral. They have bones in their bodies and many corals live together. The coral we see is actually the skeleton of coral. Because most ectodermal cells of coral secrete bones, which are formed by keratin or calcium secreted by ectoderm, there are monomers and groups in common six-release corals, and each insect is similar to an anemone. Calcareous substances secreted by ectodermal cells at the bottom of its basal plate and body wall accumulate in the bottom, side and diaphragm of insect body, as if every insect body is sitting on a lime seat, which is called coral seat. The ectoderm of the same part of colony coral can secrete calcium because the colony shape of coral is different. So their bones are stacked together in different shapes. For example, the bones of antler coral are dendritic, while the bones of brain coral are massive. They are delicious in color and can be used as high-grade decorations. Coral is very easy to reproduce. They can reproduce and grow on dead coral bones, just like corals grow taller in a year.
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/Wu Sheng /HTML/24 133