Diamonds are almost impossible to detect directly because they are so rare: very rich kimberlite pipes, the routes through which diamonds rise, may contain only three carats of diamonds per ton of kimberlite. kimberlite begins as magma in earthâs mantle (the layer between the crust and the core). as the magma smashes through layers of rock, it rips out debris, creating a mix of liquid and solid material. some of the solid material it brings up may come from a so-called diamond-stability field, where conditions of pressure and temperature are conducive to the formation of diamonds. if diamonds are to survive, though, they must shoot toward earthâs surface quickly. otherwise, they revert to graphite or burn. explorers seeking diamonds look for specks of âindicator mineralsâ peculiar to the mantle but carried up in greater quantities than diamonds and eroded out of kimberlite pipes into the surrounding land. the standard ones are garnets, chromites, and ilmenites. one can spend years searching for indicators and tracing them back to the pipes that are their source; however, 90 percent of kimberlite pipes found this way are barren of diamonds, and the rest are usually too sparse to mine. in the 1970âs the process of locating profitable pipes was refined by focusing on the subtle differences between the chemical signatures of indicator minerals found in diamond-rich pipes as opposed to those found in barren pipes. for example, g10 garnets, a type of garnet typically found in diamond-rich pipes, are lower in calcium and higher in chrome than garnets from barren pipes. geochemists john gurney showed that garnets with this composition were formed only in the diamond-stability field; more commonly found versions came from elsewhere in the mantle. gurney also found that though ilmenites did not form in the diamond-stability field, there was a link useful for prospectors: when the iron in ilmenite was highly oxidized, its source pipe rarely contained any diamonds. he reasoned that iron took on more or less oxygen in response to conditions in the kimberlitic magma itselfâmainly in response to heat and the available oxygen. when iron became highly oxidized, so did diamonds; that is, they vaporized into carbon dioxide. the primary purpose of the passage is to(a) discuss an objection to gurney's theories about the uses of indicator minerals(b) explore the formation of diamonds and the reasons for their scarcity(c) analyze the importance of kimberlite pipes in the formation of diamonds(d) define the characteristics of indicator minerals under differing conditions(e) explain a method of determining whether kimberlite pipes are likely to contain diamonds
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Geography, 23.06.2019 19:00
Study guide for unit 2 ~ lesson 3 ,4, & 5 test, thursday, january 24th lesson 3 vocabulary erosion - deposition - landform- weathering- short answers 1. how do volcanic islands form? 2.why is deposition likely to occur outside a river bend? 3. in what conditions does soil form fastest? 4. which 2 earthââŹâ˘s systems interact to form a coral island? 5. a beach growing in size is most likely the result of 6. which type of islands are formed when a chunk of land breaks off from a larger landmass? long answers explain how plants can grow in small cracks of rock that do not appear to contain soil. lesson 4 vocabulary pollution - toxic - short answers 1. most farmers pollute soil by purposefully adding 2. what is the benefit of contour plowing? . 3. using nuclear power to produce electricity can cause water pollution by 4. why do scientists predict humans will run out of fossil fuels someday? 5.farmer spray crops with fertilizer and weed killer to the crops grow. how might this affect the hydrosphere? list two different ways you use fossil fuels. 1- 2- what are two other energy sources scientists and engineers are researching? 1- 2- lesson 5 vocabulary decompose- recycling - short answers 1. which of earthââŹâ˘s systems do you interact with when you wash your hands? 2. which of earthââŹâ˘s systems is polluted by exhaust gases from buses pollute? 3. why is it important to dispose of electronic devices properly? 4. where do people interact with all four of earthââŹâ˘s systems?
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Diamonds are almost impossible to detect directly because they are so rare: very rich kimberlite pi...
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