|MadSci Network: Chemistry|
Are you (1) referring to crystals of the *same substance* grown under the *same conditions* or are you (2) wondering why crystals of different substances grow at different rates even though the conditions are the same?
If it's (2) then the answer is easy; different substances can grow at whatever rate that's dictated by their chemical nature, solubility, etc. The coincidental 'sameness' of crystallization conditions does not really have much to do with growth rate of crystals for different substances. There's just no physical basis for this expectation, sorry.
If it's (1) then you have to consider that crystallization is a stochastic process guided by supersaturation and nucleation. If you have two cases of uneven growth from the same conditions, you have to ask how many nuclei were available and are the conditions *exactly* the same. Less nuclei will result in larger crystals, and growth that's guided by the surface to volume/supersaturation ration. Lots of nuclei will results in many small crystals with huge total surface, meaning that by weight the total mass of crystals will grow faster.
Your question was posed in a way that makes further deliberation impossible. Consider asking a more specific one - maybe there's more that could be said :)
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