Re: How does temperature affect the speed crystals grow in nature or in other places?

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.