To quote from Folk: neomorphism is a broad "term of ignorance" denoting merely the change from one aspect of calcium carbonate into another, by whatever mechanism. If it is possible to determine the specific mechanism, then that more exact term should be used rather than the broad "neomorphism". Chief processes are:

  1. Inversion, whereby aragonite changes to calcite, the two minerals remaining in essential contact (in sediments nearly always with a thin water-film allowing ion-transport between host and replacer).
  2. True "recrystallization" where calcite of a particular crystal size, shape, or orientation, may be either aggrading or degrading.
  3. Strain-recrystallization wherein a strained calcite lattice transforms to a mosaic of new unstrained calcite crystals.

For details see Folk '65 SEPM SpP#13. Unfortunately, the term "recrystallization" has been used in the past for almost any method which explains the formation of sparry calcite in carbonates -even for simple cementation. Solution-cavity fill, where a large gap in time of in space separates the solution of one type of carbonate and precipitation of another type, is not considered neomorphism; it is no different than simple cementation.

Of the processes grouped under neomorphism, inversion of aragonite to calcite is probably the most important and easiest to identify. True calcite to calcite recrystallization is probably rare, although it is certainly important in some localities. Neomorphism of carbonate mud to microspar, etc., is very common-- neomorphism is the proper word here because one does not know if the original mud was aragonite (most likely) of or calcite.

Is a very slovenly and all-to-common tendency to ascribe everything one can't immediately understand either to "algae" or vaguely to "recrystallization". You should be able to show proof if recrystalization is your preferred model to explain a particular carbonate fabric.

Wednesday, March 06, 2013
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