Abstract

Dr M. H. Battey congratulated the author on the very careful and detailed study he had made of the complex sequence of changes suffered by these rocks. He would, however, also sound a note of warning. We already have dolomite as a mineral and dolomite as a rock: we now seem to be threatened with dedolomite as either a mineral or a rock, or perhaps both! If he understood the speaker correctly dedolomite is actually calcite of distinctive texture. Can we be sure that dedolomite is a good word?

The Author thanked Dr. Battey for his remarks and said that the term ‘dedolomite’, as used in this paper, refers only to the mineral product (calcite with distinct crystal fabric) of the process of dedolomitization (the replacement of dolomite by calcite) and not to the dolomite rock affected by this process. The terms ‘dedolomite’ and ‘dedolomitization’ have been adopted here for convenience of use, and also because they readily give clear indication of the nature of the original material, the replacement process and its product. Furthermore, it has already been shown that cornieules have suffered two different processes of replacement by calcite; the first process, being a replacement of gypsum, occurred at a considerable depth due to the post F4 metamorphism, while the second process occurred recently near the earth’s surface through the action of sulphate-bearing groundwater on the dolomite. Therefore, using the term ‘dedolomitization’ to describe the second process rather than ‘calcitization’ facilitates differentiation between these two processes and also

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