SUMMARY: Many phyllosilicate minerals gain greatest mechanical stability on sedimentation by orienting themselves parallel to bedding. Loss of water during the initial stages of compaction also promotes or enhances such a preferred alignment. If the mineral is then buried in the absence of tectonic stress, static mimetic recrystallization will be prompted, so that the fabric becomes metamorphic in appearance while retaining its bedding-parallel orientation.
Such a fabric, in its various stages of evolution, appears not to have received due attention in structural geology. Examples are given where problems associated with microstructures in slump sheets, the early stages of cleavage generation, the development of early schistosities and the interpretation of structural sequence, can be alleviated by the recognition of a primary fabric.