Some Uncommon Phenomena in Ptygmatic Structures

In ptygmatic structures formation of' clods' at the nodes of folds and fragmentation of the ptygma are common features. A rheological model has been set-up to generate such structural elements by considering the deforming vein to be elastic-plastic and embedded in a Newtonian viscous matrix. Because of elastic-plastic character, some regions of the vein will flow elastically and some plastically. Flow of paths of these generate complicated flow lines and with progressive deformation the vein tears off along these lines. Ptygmatic field structures have been classified and their modes of generation discussed.