|MadSci Network: Earth Sciences|
Hello, Mitchell! As with almost any real physical-chemical process, the rate of crystallization will follow what is called an Arrhenius law; that is, the rate will vary exponentially with the temperature....so long as the conditions remain favorable for crystallization to occur. In other words, if we raise the temperature too high, so that the material would normally evaporate, it will of course not crystallize at all. And, the temperature dependence will be inextricably mixed with the pressure and chemical composition of the process fluids (especially in real, natural events, as opposed to the laboratory, where we can usually vary the pressure and starting composition at will). Though increasing temperature may well increase the overall rate of crystallization, it may not result in larger crystals. Often, higher temperatures result in polycrystalline materials. That is, new crystals nucleate much faster (the nucleation process also follows an Arrhenius law) thus either the new crystals simply divide the total depositing material into a larger number (of thus smaller) crystals, or the new ones form over the old ones and stop their growth, to be stopped in turn when yet more crystals nucleate on top of them. Thus, the crystals may grow very fast, but only for a very short time, and are small. The largest natural crystals tend to grow rather slowly, actually, and may take thousands to millions of years to reach their form as exposed by mining. They may not, of course, form at an even rate, but possibly in multiple growth events distributed over that time. The issue is further complicated in natural crystallization processes by the fact that the mother liquor (from which the crystals solidify) is not likely to stay constant over time, and as a result, you may have more than one type of crystal growing. One kind may interfere with another, and so forth. Natural processes are extremely complex. If you'd like to get some appreciation of how messy they can be, you may wish to dig into the book, "The Geochemistry of Hydrothermal Ore Deposits". The deposition of ores are crystallization processes, and very relevant to your inquiry. This book is somewhat beyond your grade level, but with help from your math, chemistry, and physics teachers, you will be able to understand a large part of it.
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