Inorganic Calcite Morphology: Roles of Fluid Chemistry and Fluid Flow: DISCUSSION

Hundreds of different crystallographic forms have been recorded from natural calcite crystals. Calcite crystal aggregates exhibit a wide range of crystal fabrics whose ontogeny can be reconstructed from internal chemical zonation. It has long been hoped that this morphological diversity can be used to indicate properties of the fluid from which the calcite precipitated. Gonzfilez, Carpenter, and Lohmann (1992) add another chapter in this quest. I wish to comment on a central aspect of their paper, that is, the use of a crystal growth model to explain the mechanisms(s) controlling calcite fabric. The model, as pointed out by Gon~lez et at. (their figure 6) has been applied to carbonates for five decades. It predicts that from random nucleation on an inert planar substrate, maturation occurs during a stage of competitive growth that leads to a fabric of parallel elongate crystals. of the relationship between the c-axis and the greatest growth vector of the crystals, (2) the control of crystal form on fabric maturation, (3) the of nucleation density and growth rate, and (4) the appropriateness of applying the classic crystal growth model to speleothems.