Any division on the basis of percentage of crystal

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pseudotachylite. Any division on the basis of percentage of crystal plasticity vs brittle deformation is not practical using thin sections let alone from field observations. In addition, grain-size sensitive flow is being recognized as an important deformation mechanism in many mylonites. Thin section observation may allow more specific terms or qualifiers to be applied. A review of the historic perspective of the nomenclature and classification of fault rocks is provided in Snoke et al. (1998). Deformed ultramafic rocks have there own descriptive terminology (e.g. Boullier & Nicolas, 1975; Harte, 1977) that grew from detailed petrographic studies of kimberlite xenoliths. Many of these terms can be replaced with more general terms such as mylonite and cataclasite, and have not been re-examined by the SCMR. These examples serve to illustrate the considerable difficulties that have arisen within the SCMR in attempting to erect a practical and widely acceptable scheme. Some notes are included after particular definitions in order to explain the reasoning behind the recommended definition. In considering the definitions it is important to remember that they may be a compromise but one that is hopefully workable. All the terms given below fall into the SCMR category of ‘recommended names’ as defined by Schmid et al. (this vol.).
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