how are pearls formed?
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Natural pearls are formed more or less randomly, when some sort of irritant becomes lodged in the tissue of an oyster or mollusk. In response to the irritation, the oyster secretes nacre, a combination of calcium carbonate and organic substances, which gradually builds up in layers around the irritant. Over a period of several years, this build-up of nacre forms a pearl.\n\nThe size, shape, and color of the pearl are determined by a combination of factors, including the size and shape of the original irritant, whether the mollusk is living in salt or freshwater, and the geographic region where the mollusk lives.\n\nNatural pearls of any commercial value or desirability are extremely rare. Instead, since the early part of the 20th century, cultured pearls have supplanted natural pearls as the most common and available pearls.\n\nCultured pearls are still actual pearls, grown organically inside of oysters in the same way as natural pearls. The difference is that, in the case of cultured pearls, the pearl farmer intentionally stimulates the development of the pearl by inserting a "nucleus" into the oyster. Thus, the formation and discovery of the pearl are no longer left to chance.\n\nNatural pearls today tend to be found primarily in older jewelry from estate sales, auctions, and so forth -- in other words, existing pearls rather than new ones. However, some natural pearl beds are being increasingly harvested, including beds in the Persian Gulf area and freshwater natural pearls in the United States.
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A island is formed when underwater volcanoes erupt and cool rapidly building the hot magma onto the molten rock.  Eventually the rock keeps building upon itself and a island is risen after many years.
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A pearl is made of calcium carbonate, the same material the oyster shell that produced the pearl is made of.  Any carbonate is very susceptible to acid.  The acid in a cat's stomach is not strong enough to completely dissolve a pearl, but it will certainly etch the surface so that it is no longer glossy.
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* Spheroidizing: Spheroidite forms when plain-carbon steel is heated to approximately 700 °C for over 30 hours. Spheroidite can form at lower temperatures but the time needed drastically increases, as this is a diffusion controlled process. The result is a structure of rods or spheres of cementite within primary structure (ferrite or pearlite, depending on which side of the eutectoid you are on). The purpose is to soften higher carbon steels and allow more formability. This is the softest and most ductile form of steel. The image to the left shows where spheroidizing usually occurs.[1]\n\n    * Full annealing: Plain-carbon steel is heated to approximately 40 °C above Ac3 or Ac1 for 1 hour; this assures all the ferrite transforms into austenite (although cementite still might exist if the carbon content is greater than the eutectoid). The steel must then be cooled slowly, in the realm of 100 °F per hour. Usually it is just furnace cooled, where the furnace is turned off with the steel still inside. This results in a coarse pearlitic °structure, which means the "bands" of pearlite are thick. Fully annealed steel is soft and ductile, with no internal stresses, which is often necessary for cost-effective forming. Only spheroidized steel is softer and more ductile.[2]\n\n    * Process annealing: A process used to relieve stress in a cold-worked plain-carbon steel with less than 0.3 wt% C. The steel is usually heated up to 550 - 650°C for 1 hour, but sometimes temperatures as high as 700°C. The image to the right shows the area where process annealing occurs.[2]\n\n    * Normalizing: Plain-carbon steel is heated to approximately 55 °C above Ac3 or Acm for 1 hour; this assures the steel completely transforms to austenite. The steel is then air cooled, which is a cooling rate of approximately 100°F per minute. This results in a fine pearlitic structure, and a more uniform structure. Normalized steel has a higher strength than annealed steel; it has a relatively high strength and ductility.[3]\n\n    * Quenching: Plain-carbon steel with at least 0.4 wt% C is heated to normalizing temperatures and then rapidly cooled (quenched) in water, brine, or oil to the critical temperature. The critical temperature is dependent on the carbon content, but as a general rule is lower as the carbon content increases. This results in a martensitic structure; a form of steel that possesses a super-saturated carbon content in a deformed Body Centered Cubic (BCC) crystalline structure, properly termed Body Centered Tetragonal (BCT). This crystalline structure has a very high amount of internal stress. Due to these internal stress quenched steel is extremely hard but brittle, usually too brittle for practical purposes. These internal stresses cause stress cracks on the surface. Quenched steel is approximately three (lower carbon content) to four(high carbon content) times harder than normalized steel.[4]\n          o Martempering (Marquenching): The marquenching process is the same as quenching, but the steel is quenched in an oil or brine solution at a temperature right above the "martensite start temperature". The steel is held in this solution until the center and surface temperatures equalize. Then the steel is cooled at a moderate speed to keep the temperature gradient minimal. Not only does this process reduce internal stresses and stress cracks, but it also increases the impact resistance. This is the quenching process used in industry to obtain martensite.[5]\n\n    * Quench and tempering: This is the most common heat treatment encountered, because the final properties can be precisely determined by the temperature and time of the tempering. Tempering involves reheating quenched steel to a temperature below the eutectoid temperature then cooling. The elevated temperature allows very small amounts of spheroidite to form, which restore ductility, but reduces hardness. Actual temperatures and times are carefully chosen for
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The atomic and molecular structure of each mineral determines the crystal shape. Each mineral is composed of a specific molecular compound, and those molecules arrange themselves in an ordered fashion based on their structure that will form a crystal.  \n\nThese regular and repeating groups of molecules and atoms form a unit that is known as a lattice. There are 14 lattice groups (Bravais lattices), which fall into six (some crystallographers use seven) different crystal systems. Each crystal system includes the different rotation and reflection symmetries around a fixed lattice point. \n\nTo make this all more confusing, and to the horror of most mineralogy students there are also 32 different crystal classes. Each crystal class is a different and unique set of symmetrical forms.\n\nTo see illustrations of Bravais Lattices go here:\nhttp://hyperphysics.phy-astr.gsu.edu/hbase/solids/bravais.html\n\nFor a more detailed explanation go here:\nhttp://dave.ucsc.edu/myrtreia/crystal.html#INTRO
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because the shell is formed by the animals ribs which have expanded outward and fused together. i didn't believe it at first when my diversity teacher told me but i recalled a turtle shell i had as a child and when you looked inside the vertebral column was fused to the top of the shell which makes sense when you consider the rib expansion factor.
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The hard, rigid outer covering of certain animals is called a shell. While many animals, particularly those that live in the sea, produce exoskeletons, usually only those of mollusks are considered to be shells. It is sometimes erroneously claimed that shells are made of chitin, but these are unrelated materials (except for their hardness and use as a covering by animals).\n\nThe shell is usually made of nacre, an organic mixture of outer layers of horny conchiolin (a scleroprotein), followed by an intermediate layer of calcite oraragonite, and then a layer of calcium carbonate (CaCO3) in the form of platy crystals.\n\nNacre is secreted by the epithelial cells (formed by the germ layer ectoderm) of the mantle tissue of certain species of mollusk. Mollusk blood is rich in a liquid form of calcium. In these mollusks the calcium is concentrated out from the blood where it can crystallize as calcium carbonate. The individual crystals of each layer differ in shape and orientation. Nacre is continually deposited onto the inner surface of the animal's shell (the iridescent nacreous layer also known as mother of pearl), both as a means to smoothen the shell itself and as a defense against parasitic organisms and damaging detritus.\n\n \nVarious seashellsWhen a mollusk is invaded by a parasite or is irritated by a foreign object that the animal cannot eject, a process known as encystation entombs the offending entity in successive, concentric layers of nacre. This process eventually forms what we call pearls and continues for as long as the mollusk lives.\n\nShells are very durable and outlast the otherwise soft-bodied animals that produce them by a very long time. Large amounts of shells may form sediment and become compressed into limestone. Shells that wash up on beaches are called seashells, and are collected by some enthusiasts
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Basically one of three ways. These are extrusion, intrusion, and accretion. \n\nExtrusion is the process of volcanism. Volcanoes erupt molten rock that may have originated as subducted oceanic crust or deeper rock. This magma adds huge volumes of rock to the crust as it erupts and cools into solid rock. \n\nIntrusion is a similar process, but no eruption takes place. Large bodies of molten rock float upward over long time periods through the crust. When these cool and harden they are called plutons or batholiths (depending on size-batholiths are larger). These form large parts of the crust.\n\nAccretion is the other method. In some instances plate tectonics can force oceanic plates up and over continental plates. These often form what are called ophiolites where we can examine oceanic crust on dry land. Large parts of continents or islands are often forced against continental plates. This can force sediments and oceanic crust upward creating what are called 'accretionary terrane'. Much of California is an accretionary terrane, built of islands in a fore arc subduction zone that were forced up against a paleocoastline that once was near the eastern border of present day California. \n\nHere two other explanations similar to my own that illustrate these processes:\nhttp://www.physicalgeography.net/fundamentals/10j.html\nhttp://earth.leeds.ac.uk/assyntgeology/extra_info/ehistory.htm
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Check the link below.  It can be formed through volcanic activity as well as crystallizing out of mineral rich water deposits.  It is almost pure iron that is oxidized.
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Beryllium gets very hot such as near a volcano.\n\n\nNot all Emeralds are formed in a hydrothermal vein. Some Emeralds are formed in pegmatite deposits. Pegmatites are similar to hydrothermal veins, except that the primary agent in hydrothermal vein formation is hot water and the primary agent in pegmatites is magma, or molten rock. As this magma begins to cool, some elements are left in solution in the remaining fluid. When the necessary elements are present and if conditions are perfect, Emerald crystal formation may occur in these pegmatites.
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If you mean how did they form...\n\nOpals form from hydrothermal solutions containing silicon dioxide. That simply means heated water containing dissolved quartz.\n\nThese solutions are deposited in sedimentary rocks where they come out of solution. Sedimentary rock is where you find opals.\n\nOpals contain small amounts of water in its structure. That is what gives it its "play of colors".\n\nIt is often referred to as hydrated silica & is called cryptocrystalline quartz because it is essentially quartz without a crystal structure.\n\nSome of the world's most beautiful opals come from Australia & Mexico. The ones found in Mexico often have a reddish "play of colors" & is called fire opal.
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You'll have to consult a geology textbook to get a good answer on this.\n\nBasic answer: The shapes that the molecules take when they come together to form minerals, form in regular patterns.  That is, they align very regularly next to the last molecule.  The angles that these bond also form the angles at which the minerals form and cleve.
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The major way gold nuggets are formed is by being dissolved in hot water solutions that percolate through rocks. The solubility of gold is enhanced by chloride ions. When this hot water encounters changed conditions (such as cooling or mixing with other water) the gold can exceed its solubility in water and be precipitated. The water circulation about intrusions or extrusions of volcanic rocks often provides the energy to drive this process.\n \nAnother way of concentrating gold into nuggets is by biological activity. Some bacteria are known to be able to concentrate the gold from dilute solutions.
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D. formation of micelles\n\nMicelles only form when the concentration of surfactant is greater than the critical micelle concentration (CMC).
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Probably white.  But, double check that a pearl is even a mineral - I don't remember that, but it's been a while
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Erosion breaks up igneous and metamorphic rocks, and the particles build up to create sedimentary rocks.  \n\nHope this is helpful.
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That's a good question. I'm quite sure "God made it" isn't the answer you're looking for, especially since you posted this in the science section. \n\nReligion seems to have all the answers, but those answers never satisfy the appetite of curiosity and learning. Below are several different worded versions of the same basic theory of how the Earth (and other planets) formed. \n\nBe sure to check out the sources.\n\n1. The planets formed from the material left over as a result of our sun's formation. As the nebulous cloud condensed and began to rotate, most of the gas condensed into what is now our sun. The remaining material formed what is now the planets and the other bodies in our solar system.\n\n2. The prevailing theory is that they are formed from those remnants of a nebula that do not condense under gravity to form a protostar. Instead, these remnants become a thin disc of dust and gas revolving around the protostar and begin to condense about local concentrations of mass within the disc. These concentrations become ever more dense until they collapse inward under gravity to form protoplanets. When the protostar has grown such that it ignites to form a star, its solar wind blows away most of the disc's remaining material. Thereafter there still may be many protoplanets orbiting the star or each other, but over time many will collide, either to form a single larger planet or release material for other larger protoplanets or planets to absorb. Meanwhile, protoplanets that have avoided collisions may become moons of larger planets.\n\n3. The most widely accepted model for the origin of the Solar System is called the  nebula theory. Most generally phrased, the theory states that the Solar System condensed from a large, lumpy cloud of cold gas and dust.\n\n4. Solar Nebula Theory