Recrystallization is an essentially physical process that has meanings in chemistry and geology.
In chemistry, recrystallization is a procedure for purifying compounds. A typical situation is that a desired compound X is contaminated by a small amount of compound Y. A chemist can prepare a saturatedsolution of the mixture X+Y in a warm solvent and subsequently lower the temperature. For most compounds, the solubility decreases with decreasing temperature. If X and Y have approximately equal solubilities, then X will precipitate while Y stays in solution. The precitipate now has a much higher purity than the original mixture. The cost of this purification method is the loss of the part of compound X that stays in solution.
In geology, solid-state recrystallization is a metamorphic process that occurs under situations of intense temperature and pressure where grains, atoms or molecules of a rock or mineral are packed closer together, creating a new crystal structure. The basic composition remains the same. This process can be illustrated by observing how snow recrystallizes to ice without melting. As opposed to metasomatism, which is a chemical change caused by metamorphism, recrystallization is a physical process. However, recrystallization can occur when a local migration of chemicals results in the chemical change of the rock or mineral with no external addition of materials.
In metallurgy, recrystallization is the growth of particular grain fragments in a metal or alloy at the expense of others. This occurs when the metal or alloy is severely worked, as by cold rolling. Recrystallization results in greater, strain-free grains.
Recrystallization is an often-used method for purifying solids.
Recrystallization works by taking advantage of the different solubility properties of compounds, and allows impurities to be removed from crude solids.
When choosing a solvent for recrystallization, the impure compound should have poor solubility in the solvent at low temperatures but be completely soluble at high temperatures.
I was essentially concerned with the mechanics of growth of isolated matrix mica flakes under conditions involving annealing recrystallization, and not with the mechanism of chemical transport involved in chemical differentiation, which will be attempted elsewhere.
My point, however, that in mimetic recrystallizationmica flakes grow so as to become stain-free is amply illustrated by Dr. Nicholson's photographs.
My other point that at a subsequent stage of recrystallizationmica flakes grow parallel to axial planes of folds is again shown by Dr. Nicholson's Fig.
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